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+
+</style>
+<h1 id="http-support"><a class="header" href="#http-support">HTTP Support</a></h1>
+<p>NNG offers support for creation of HTTP clients, and servers. NNG supports HTTP/1.1 at present, and supports
+a subset of functionality, but the support should be sufficient for simple clients, REST API servers, static content servers,
+and gateways between HTTP and and other protocols. It also provides support for WebSocket based connections.</p>
+<p>HTTP follows a request/reply model, where a client issues a request, and the server is expected to reply.
+Every request is answered with a single reply.</p>
+<h2 id="header-file"><a class="header" href="#header-file">Header File</a></h2>
+<pre><code class="language-c">#include &lt;nng/http.h&gt;
+</code></pre>
+<p>Unlike the rest of NNG, the HTTP API in NNG requires including <code>nng/http.h</code>. It is not necessary to include
+the main <code>nng/nng.h</code> header, it will be included transitively by <code>nng/http.h</code>.</p>
+<h2 id="connection-object"><a class="header" href="#connection-object">Connection Object</a></h2>
+<pre><code class="language-c">typedef struct nng_http nng_http;
+</code></pre>
+<p>The <a name="a001"></a><code>nng_http</code> object represents a single logical HTTP connection to the server.
+For HTTP/1.1 and earlier, this will correspond to a single TCP connection, but the object
+also contains state relating to the transaction, such as the hostname used, HTTP method used,
+request headers, response status, response headers, and so forth.</p>
+<p>An <code>nng_http</code> object can be reused, unless closed, so that additional transactions can be
+performed after the first transaction is complete.</p>
+<p>At any given point in time, an <code>nng_http</code> object can only refer to a single HTTP transaction.
+In NNG, these <code>nng_http</code> objects are used in both the client and server APIs.</p>
+<p>The <code>nng_http</code> object is created by either <a href="/api/http.html#creating-connections"><code>nng_http_client_connect</code></a> or by an HTTP server
+object which then passes it to an [<code>nng_http_handler</code>] callback function.</p>
+<h3 id="http-method"><a class="header" href="#http-method">HTTP Method</a></h3>
+<pre><code class="language-c">void nng_http_set_method(nng_http *conn, const char *method);
+const char *nng_http_get_method(nng_http *conn);
+</code></pre>
+<p>Each HTTP transaction has a single verb, or method, that is used. The most common methods are “GET”, “HEAD”, and “POST”,
+but a number of others are possible.</p>
+<p>The <a name="a002"></a><code>nng_http_set_method</code> function specifies the HTTP method to use for the transaction.
+The default is “GET”. HTTP methods are case sensitive, and generally upper-case, such as “GET”, “POST”, “HEAD”,
+and so forth. This function silently truncates any method to 32-characters. (There are no defined methods longer than this.)</p>
+<p>The <a name="a003"></a><code>nng_http_get_method</code> function is used, typically on a server, to retrieve the method the client
+set when issuing the transaction.</p>
+<h3 id="http-uri"><a class="header" href="#http-uri">HTTP URI</a></h3>
+<pre><code class="language-c">int nng_http_set_uri(nng_http *conn, const char *uri, const char *query);
+const char *nng_http_get_uri(nng_http *conn);
+</code></pre>
+<p>The <a name="a004"></a><code>nng_http_set_uri</code> function sets the <a name="a005"></a>URI, which normally appears like a path such as “/docs/index.html”,
+for the next transaction on <em>conn</em>. It sets the URI to <em>uri</em>, and, if <em>query</em> is not <code>NULL</code>, also appends the
+contents of <em>query</em>, separated by either the ‘?’ or ‘&amp;’ character, depending on whether <em>uri</em> already
+contains a query string. It may return <a href="/api/errors.html#NNG_ENOMEM"><code>NNG_ENOMEM</code></a>, or <a href="/api/errors.html#NNG_EMSGSIZE"><code>NNG_EMSGSIZE</code></a> if the the result is too long,
+or <a href="/api/errors.html#NNG_EINVAL"><code>NNG_EINVAL</code></a> if there is some other problem with the URI.</p>
+<div class="mdbook-alerts mdbook-alerts-note">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ note
+</p>
+<p>The <em>uri</em> and <em>query</em> must be already percent-encoded if necessary.</p>
+</div>
+<p>The <a name="a006"></a><code>nni_http_get_uri</code> function is used to obtain the URI that was previously set by <code>nng_http_set_uri</code>.
+If the URI is unset (such as for a freshly created connection), then it returns <code>NULL</code>. The returned value
+will have any query concentated, for example “/api/get_user.cgi?name=garrett”.</p>
+<h3 id="http-version"><a class="header" href="#http-version">HTTP Version</a></h3>
+<pre><code class="language-c">int nng_http_set_version(nng_http *conn, const char *version);
+const char *nng_http_get_version(nng_http *conn);
+</code></pre>
+<p>The <a name="a007"></a><code>nng_http_set_version</code> function is used to select the HTTP protocol version to use for the
+exchange. At present, only the values <code>NNG_HTTP_VERSION_1_0</code> and <code>NNG_HTTP_VERSION_1_1</code> (corresponding to
+“HTTP/1.0” and “HTTP/1.1”) are supported. NNG will default to using “HTTP/1.1” if this function is not called.
+If an unsupported version is supplied, <a href="/api/errors.html#NNG_ENOTSUP"><code>NNG_ENOTSUP</code></a> will be returned, otherwise zero.</p>
+<p>The <a name="a008"></a><code>nng_http_get_version</code> function is used to determine the version the client selected. Normally
+there is little need to use this, but there are some subtle semantic differences between HTTP/1.0 and HTTP/1.1.</p>
+<div class="mdbook-alerts mdbook-alerts-tip">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ tip
+</p>
+<p>There are few, if any, remaining HTTP/1.0 implementations that are not also capable of HTTP/1.1.
+It might be easiest to just fail any request coming in that is not HTTP/1.1.</p>
+</div>
+<div class="mdbook-alerts mdbook-alerts-note">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ note
+</p>
+<p>NNG does not support HTTP/2 or HTTP/3 at this time.</p>
+</div>
+<h3 id="http-status"><a class="header" href="#http-status">HTTP Status</a></h3>
+<pre><code class="language-c">uint16_t nng_http_get_status(nng_http *conn);
+const char *nng_http_get_reason(nng_http_conn *conn);
+void nng_http_set_status(nng_http *conn, uint16_t status, const char *reason);
+</code></pre>
+<p>The <a name="a009"></a><code>nng_http_get_status</code> function obtains the numeric code (typipcally numbered from 100 through 599) returned
+by the server in the last exchange on <em>conn</em>. (If no exchange has been performed yet, the result is undefined.)</p>
+<p>A descriptive message matching the status code is returned by <a name="a010"></a><code>nng_http_get_reason</code>.</p>
+<p>The <a name="a011"></a><code>nng_http_set_status</code> function is used on a server in a handler callback to set the status codethat will be
+reported to the client to <em>status</em>, and the associated text (reason) to <em>reason</em>. If <em>reason</em> is <code>NULL</code>,
+then a built in reason based on the <em>status</em> will be used instead.</p>
+<div class="mdbook-alerts mdbook-alerts-tip">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ tip
+</p>
+<p>Callbacks used on the server may wish to use <a href="/TODO.html"><code>nng_http_server_set_error</code></a> or <a href="/TODO.html"><code>nng_http_server_set_redirect</code></a> instead of
+<code>nng_http_set_status</code>, because those functions will also set the response body to a suitable HTML document
+for display to users.</p>
+</div>
+<p>Status codes are defined by the IETF. Here are defininitions that NNG provides for convenience:</p>
+<div class="table-wrapper"><table><thead><tr><th>Name</th><th>Code</th><th>Reason Text</th><th>Notes</th></tr></thead><tbody>
+<tr><td><code>NNG_HTTP_STATUS_CONTINUE</code><a name="#NNG_HTTP_STATUS_CONTINUE"></a></td><td>100</td><td>Continue</td><td>Partial transfer, client may send body.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_SWITCHING</code><a name="#NNG_HTTP_STATUS_SWITCHING"></a></td><td>101</td><td>Switching Protocols</td><td>Used when upgrading or hijacking a connection.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_PROCESSING</code><a name="#NNG_HTTP_STATUS_PROCESSING"></a></td><td>102</td><td>Processing</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_OK</code><a name="#NNG_HTTP_STATUS_OK"></a></td><td>200</td><td>OK</td><td>Successful result.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_CREATED</code><a name="#NNG_HTTP_STATUS_CREATED"></a></td><td>201</td><td>Created</td><td>Resource created successfully.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_ACCEPTED</code><a name="#NNG_HTTP_STATUS_ACCEPTED"></a></td><td>202</td><td>Created</td><td>Request accepted for future processing.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_NOT_AUTHORITATIVE</code><a name="#NNG_HTTP_STATUS_NOT_AUTHORITATIVE"></a></td><td>203</td><td>Not Authoritative</td><td>Request successful, but modified by proxy.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_NO_CONTENT</code><a name="#NNG_HTTP_STATUS_NO_CONTENT"></a></td><td>204</td><td>No Content</td><td>Request successful, no content returned.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_RESET_CONTENT</code><a name="#NNG_HTTP_STATUS_NO_CONTENT"></a></td><td>205</td><td>Reset Content</td><td>Request successful, client should reload content.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_PARTIAL_CONTENT</code><a name="#NNG_HTTP_STATUS_NO_CONTENT"></a></td><td>206</td><td>Partial Content</td><td>Response to a range request.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_MULTI_STATUS</code><a name="#NNG_HTTP_STATUS_MULTI_STATUS"></a></td><td>207</td><td>Multi-Status</td><td>Used with WebDAV.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_ALREADY_REPORTED</code><a name="#NNG_HTTP_STATUS_ALREADY_REPORTED"></a></td><td>208</td><td>Already Reported</td><td>Used with WebDAV.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_IM_USED</code><a name="#NNG_HTTP_STATUS_IM_USED"></a></td><td>226</td><td>IM Used</td><td>Used with delta encodings, rarely supported.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_MULTIPLE_CHOICES</code><a name="#NNG_HTTP_STATUS_MULTIPLE_CHOICES"></a></td><td>300</td><td>Multiple Choices</td><td>Multiple responses possible, client should choose.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_MOVED_PERMANENTLY</code><a name="#NNG_HTTP_STATUS_MOVED_PERMANENTLY"></a></td><td>301</td><td>Moved Permanently</td><td>Permanent redirection, may be saved by client.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_FOUND</code><a name="#NNG_HTTP_STATUS_FOUND"></a></td><td>302</td><td>Found</td><td>Temporary redirection, client may switch to GET.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_SEE_OTHER</code><a name="#NNG_HTTP_STATUS_SEE_OTHER"></a></td><td>303</td><td>See Other</td><td>Redirect, perhaps after a success POST or PUT.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_NOT_MODIFIED</code><a name="#NNG_HTTP_STATUS_NOT_MODIFIED"></a></td><td>304</td><td>Not Modified</td><td>Resource not modified, client may use cached version.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_USE_PROXY</code><a name="#NNG_HTTP_STATUS_USE_PROXY"></a></td><td>305</td><td>Use Proxy</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_TEMPORARY_REDIRECT</code><a name="#NNG_HTTP_STATUS_TEMPORARY_REDIRECT"></a></td><td>307</td><td>Temporary Redirect</td><td>Temporary redirect, preserves method.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_PERMANENT_REDIRECT</code><a name="#NNG_HTTP_STATUS_PERMANENT_REDIRECT"></a></td><td>308</td><td>Permanent Redirect</td><td>Permanent redirect.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_BAD_REQUEST</code><a name="#NNG_HTTP_STATUS_BAD_REQUEST"></a></td><td>400</td><td>Bad Request</td><td>Generic problem with the request.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_UNAUTHORIZED</code><a name="#NNG_HTTP_STATUS_UNAUTHORIZED"></a></td><td>401</td><td>Unauthorized</td><td>Indicates a problem with authentication.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_PAYMENT_REQUIRED</code><a name="#NNG_HTTP_STATUS_PAYMENT_REQUIRED"></a></td><td>402</td><td>Payment Required</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_FORBIDDEN</code><a name="#NNG_HTTP_STATUS_FORBIDDEN"></a></td><td>403</td><td>Forbidden</td><td>No permission to access resource.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_NOT_FOUND</code><a name="#NNG_HTTP_STATUS_NOT_FOUND"></a></td><td>404</td><td>Not Found</td><td>Resource does not exist.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_METHOD_NOT_ALLOWED</code><a name="#NNG_HTTP_STATUS_METHOD_NOT_ALLOWED"></a></td><td>405</td><td>Method Not Allowed</td><td>Resource does not support the method.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_METHOD_NOT_ACCEPTABLE</code><a name="#NNG_HTTP_STATUS_METHOD_NOT_ACCEPTABLE"></a></td><td>406</td><td>Not Acceptable</td><td>Could not satisfy accept requirements.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_PROXY_AUTH_REQUIRED</code><a name="#NNG_HTTP_STATUS_PROXY_AUTH_REQUIRED"></a></td><td>407</td><td>Proxy Authentication Required</td><td>Proxy requires authentication.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_REQUEST_TIMEOUT</code><a name="#NNG_HTTP_STATUS_REQUEST_TIMEOUT"></a></td><td>408</td><td>Request Timeout</td><td>Timed out waiting for request.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_CONFLICT</code><a name="#NNG_HTTP_STATUS_CONFLICT"></a></td><td>409</td><td>Conflict</td><td>Conflicting request.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_GONE</code><a name="#NNG_HTTP_STATUS_GONE"></a></td><td>410</td><td>Gone</td><td>Resource no longer exists.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_LENGTH_REQUIRED</code><a name="#NNG_HTTP_STATUS_LENGTH_REQUIRED"></a></td><td>411</td><td>Length Required</td><td>Missing Content-Length.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_PRECONDITION_FAILED</code><a name="#NNG_HTTP_STATUS_PRECONDITION_FAILED"></a></td><td>412</td><td>Precondition Failed</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_CONTENT_TOO_LARGE</code><a name="#NNG_HTTP_STATUS_PAYLOAD_TOO_LARGE"></a></td><td>413</td><td>Content Too Large</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_URI_TOO_LONG</code><a name="#NNG_HTTP_STATUS_URI_TOO_LONG"></a></td><td>414</td><td>URI Too Long</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_UNSUPPORTED_MEDIA_TYPE</code><a name="#NNG_HTTP_STATUS_UNSUPPORTED_MEDIA_TYPE"></a></td><td>415</td><td>Unsupported Media Type</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_RANGE_NOT_SATISFIABLE</code><a name="#NNG_HTTP_STATUS_RANGE_NOT_SATISFIABLE"></a></td><td>416</td><td>Range Not Satisfiable</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_EXPECTATION_FAILED</code><a name="#NNG_HTTP_STATUS_EXPECTATION_FAILED"></a></td><td>417</td><td>Expectation Failed</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_TEAPOT</code><a name="#NNG_HTTP_STATUS_TEAPOT"></a></td><td>418</td><td>I Am A Teapot</td><td>RFC 2324.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_UNPROCESSABLE_ENTITY</code><a name="#NNG_HTTP_STATUS_UNPROCESSABLE_ENTITY"></a></td><td>422</td><td>Unprocessable Entity</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_LOCKED</code><a name="#NNG_HTTP_STATUS_LOCKED"></a></td><td>423</td><td>Locked</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_FAILED_DEPENDENCY</code><a name="#NNG_HTTP_STATUS_FAILED_DEPEDNENCY"></a></td><td>424</td><td>Failed Dependency</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_TOO_EARLY</code><a name="#NNG_HTTP_STATUS_TOO_EARLY"></a></td><td>425</td><td>Too Early</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_UPGRADE_REQUIRED</code><a name="#NNG_HTTP_STATUS_UPGRADE_REQUIRED"></a></td><td>426</td><td>Upgrade Required</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_PRECONDITION_REQUIRED</code><a name="#NNG_HTTP_STATUS_PRECONDITION_REQUIRED"></a></td><td>428</td><td>Precondition Required</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_TOO_MANY_REQUESTS</code><a name="#NNG_HTTP_STATUS_TOO_MANY_REQUESTS"></a></td><td>429</td><td>Too Many Requests</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_HEADERS_TOO_LARGE</code><a name="#NNG_HTTP_STATUS_HEADERS_TOO_LARGE"></a></td><td>431</td><td>Headers Too Large</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_UNAVAIL_LEGAL_REASONS</code><a name="#NNG_HTTP_STATUS_UNAVAIL_LEGAL_REASONS"></a></td><td>451</td><td>Unavailabe For Legal Reasons</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_INTERNAL_SERVER_ERROR</code><a name="#NNG_HTTP_STATUS_INTERNAL_SERVER_ERROR"></a></td><td>500</td><td>Internal Server Error</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_NOT_IMPLEMENTED</code><a name="#NNG_HTTP_STATUS_NOT_IMPLEMENTED"></a></td><td>501</td><td>Not Implemented</td><td>Server does not implement method.</td></tr>
+<tr><td><code>NNG_HTTP_STATUS_BAD_GATEWAY</code><a name="#NNG_HTTP_STATUS_BAD_GATEWAY"></a></td><td>502</td><td>Bad Gateway</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_SERVICE_UNAVAILALE</code><a name="#NNG_HTTP_STATUS_SERVICE_UNAVAILABLE"></a></td><td>503</td><td>Service Unavailable</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_GATEWAY_TIMEOUT</code><a name="#NNG_HTTP_STATUS_GATEWAY_TIMEOUT"></a></td><td>504</td><td>Gateway TImeout</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_HTTP_VERSION_NOT_SUPP</code><a name="#NNG_HTTP_STATUS_HTTP_VERSION_NOT_SUPP"></a></td><td>505</td><td>HTTP Version Not Supported</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_VARIANT_ALSO_NEGOTIATES</code><a name="#NNG_HTTP_STATUS_VARIANT_ALSO_NEGOTIATES"></a></td><td>506</td><td>Variant Also Negotiates</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_INSUFFICIENT_STORAGE</code><a name="#NNG_HTTP_STATUS_INSUFFICIENT_STORAGE"></a></td><td>507</td><td>Variant Also Negotiates</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_LOOP_DETECTED</code><a name="#NNG_HTTP_STATUS_LOOP_DETECTED"></a></td><td>508</td><td>Loop Detected</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_NOT_EXTENDED</code><a name="#NNG_HTTP_STATUS_NOT_EXTENDED"></a></td><td>510</td><td>Not Extended</td><td></td></tr>
+<tr><td><code>NNG_HTTP_STATUS_NETWORK_AUTH_REQUIRED</code><a name="#NNG_HTTP_STATUS_NETWORK_AUTH_REQUIRED"></a></td><td>511</td><td>Network Authentication Required</td><td></td></tr>
+</tbody></table>
+</div>
+<h3 id="retrieving-headers"><a class="header" href="#retrieving-headers">Retrieving Headers</a></h3>
+<pre><code class="language-c">const char *nng_http_get_header(nng_http *conn, const char *key);
+bool nng_next_header(nng_http *conn, const char **keyp, const char **valuep, void **next);
+</code></pre>
+<p>The <a name="a012"></a><code>nng_http_get_header</code> returns the header value matching <em>key</em> that was received over <em>conn</em>,
+or <code>NULL</code> if no such header exists.</p>
+<p>Thus, if <em>conn</em> is a client connection, then this function returns the the header value
+sent by the server as part of a response, whereas if it is a server connection, it returns
+the header value sent by the client as part of the request.</p>
+<p>If multiple headers are present with the same key, they may be returned as a combined value,
+with individual values separated by commas, but this behavior is not guaranteed.</p>
+<p>The <a name="a013"></a><code>nng_http_next_header</code> function iterates over all the headers, using the same list
+that <code>nng_http_get_header</code> uses. To start, it is called with <em>next</em> initialized to <code>NULL</code>.
+If a header was found, then it returns <code>true</code>, and sets <em>keyp</em> and <em>valuep</em> to values containing
+the header name and value. It also updates <em>next</em>, which should be used for the next iteration.</p>
+<p>Once <code>nng_http_next_header</code> returns <code>false</code>, further calls with the same parameters will continue to do so.
+The scan can be rest by setting <em>next</em> to <code>NULL</code>.</p>
+<h3 id="modifying-headers"><a class="header" href="#modifying-headers">Modifying Headers</a></h3>
+<pre><code class="language-c">int nng_http_add_header(nng_http *conn, const char *key, const char *val);
+int nng_http_set_header(nng_http *conn, const char *key, const char *val);
+void nng_http_del_header(nng_http *conn, const char *key);
+</code></pre>
+<p>The <a name="a014"></a><code>nng_http_add_header</code>, <a name="a015"></a><code>nng_http_set_header</code>, and <a name="a016"></a><code>nng_http_del_header</code> functions are
+used to add a modify either the request or response headers for <em>conn</em> prior to sending to the connected peer on <em>conn</em>.</p>
+<p>Thus, if the <em>conn</em> is a client connection created by <a href="/api/http.html#creating-connections"><code>nng_http_client_connect</code></a>, then the request headers are modified.
+Conversely, if it is a connection created by an HTTP server and used in a callback function, then the response headers are modified.</p>
+<p>The <code>nng_http_add_header</code> function adds a header with the name <em>key</em>, and the value <em>val</em>, to the list of headers.
+In so doing, it may bring collapse multiple headers with the same name into a comma separated list, following
+the syntax specified in RFC 9110. The function may return <a href="/api/errors.html#NNG_ENOMEM"><code>NNG_ENOMEM</code></a>, <a href="/api/errors.html#NNG_EMSGSIZE"><code>NNG_EMSGSIZE</code></a>, or <a href="/api/errors.html#NNG_EINVAL"><code>NNG_EINVAL</code></a>.</p>
+<p>The <code>nng_http_set_header</code> function adds the header if it does not already exist, but replaces any and all previously existing
+headers with the same name <em>key</em>, if they exist. In all other respects it behaves similarly to <code>nng_http_add_header</code>.</p>
+<p>The <code>nng_http_del_header</code> removes all headers with name <em>key</em>.</p>
+<div class="mdbook-alerts mdbook-alerts-note">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ note
+</p>
+<p>Some HTTP headers have special semantics, such as the “Host”, “Content-Length”, and “Content-Type” headers.
+This implementation may apply those semantics, in order to conform to the specifications for HTTP, such
+as by guaranting that only a single instance of one of these headers is present.</p>
+</div>
+<h3 id="retrieving-body-content"><a class="header" href="#retrieving-body-content">Retrieving Body Content</a></h3>
+<pre><code class="language-c">void nng_http_get_body(nng_http_conn *conn, void **datap, size_t *sizep);
+</code></pre>
+<p>The <a name="a017"></a><code>nng_http_get_data</code> obtains the most recently received request or
+response body. This will be <code>NULL</code> if the content has not been retrieved
+properly yet, or if the peer did not any content. (Some requests are defined
+to never have body content, such as “HEAD”.)</p>
+<h3 id="storing-body-content"><a class="header" href="#storing-body-content">Storing Body Content</a></h3>
+<pre><code class="language-c">void nng_http_set_body(nng_http_conn *conn, void *data, size_t size);
+void nng_http_copy_body(nng_http_conn *conn, const void *data, size_t size);
+</code></pre>
+<p>The <a name="a018"></a><code>nng_http_set_data</code> function sets the outgoing body content to <em>data</em>,
+which must be <em>size</em> bytes long. The caller must ensure that <em>data</em> remains
+valid for the duration of the transaction.</p>
+<p>The <a name="a019"></a><code>nng_http_copy_data</code> function makes a copy of <em>data</em>, which
+will be freed automatically when the transaction is finished, but otherwise
+behaves like <code>nng_http_set_data</code>.</p>
+<p>On client <em>conn</em> objects, these functions update the request object, but on server
+<em>conn</em> objects, they update the response object.</p>
+<p>These functions also update the relevant “Content-Length” header.</p>
+<div class="mdbook-alerts mdbook-alerts-note">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ note
+</p>
+<p>The current framework does not support sending data via chunked
+transfer-encoding.</p>
+</div>
+<div class="mdbook-alerts mdbook-alerts-tip">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ tip
+</p>
+<p>It is a good idea to also set the <code>Content-Type</code> header.</p>
+</div>
+<h3 id="closing-the-connection"><a class="header" href="#closing-the-connection">Closing the Connection</a></h3>
+<pre><code class="language-c">void nng_http_close(nng_http *conn);
+</code></pre>
+<p>The <a name="a020"></a><code>nng_http_close</code> function closes the supplied HTTP connection <em>conn</em>,
+including any disposing of any underlying file descriptors or related resources.</p>
+<p>Once this function, no further access to the <em>conn</em> structure may be made.</p>
+<h3 id="reset-connection-state"><a class="header" href="#reset-connection-state">Reset Connection State</a></h3>
+<pre><code class="language-c">void nng_http_reset(nng_http *conn);
+</code></pre>
+<p>The <a name="a021"></a><code>nng_http_reset</code> function resets the request and response state of the
+the connection <em>conn</em>, so that it is just as if it had been freshly created with
+<a href="/api/http.html#creating-connections"><code>nng_http_client_connect</code></a> or passed into a handler function for a server callback.</p>
+<p>The intended purpose of this function is to clear the object state before reusing the <em>conn</em> for
+subsequent transactions.</p>
+<h3 id="direct-read-and-write"><a class="header" href="#direct-read-and-write">Direct Read and Write</a></h3>
+<pre><code class="language-c">void nng_http_read(nng_http *conn, nng_aio *aio);
+void nng_http_write(nng_http *conn, nng_aio *aio);
+void nng_http_read_all(nng_http *conn, nng_aio *aio);
+void nng_http_write_all(nng_http *conn, nng_aio *aio);
+</code></pre>
+<p>The <a name="a022"></a><code>nng_http_read</code> and <a name="a023"></a><code>nng_http_write</code> functions read or write data asynchronously from or to the
+connection <em>conn</em>, using the <a href="/api/aio.html#scatter-gather-vectors"><code>nng_iov</code></a> that is set in <em>aio</em> with <a href="/api/aio.html#scatter-gather-vectors"><code>nng_aio_set_iov</code></a>.
+These functions will complete as soon as any data is transferred.
+Use <a href="/api/aio.html#result-of-operation"><code>nng_aio_count</code></a> to determine how much data was actually transferred.</p>
+<p>The <a name="a024"></a><code>nng_http_read_all</code> and <a name="a025"></a><code>nng_http_write_all</code> functions perform the same task, but will keep resubmitting
+operations until the the entire amount of data requested by the <a href="/api/aio.html#scatter-gather-vectors"><code>nng_iov</code></a> is transferred.</p>
+<div class="mdbook-alerts mdbook-alerts-note">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ note
+</p>
+<p>These functions perform no special handling for chunked transfers.</p>
+</div>
+<p>These functions are most likely to be useful after hijacking the connection with <a href="/api/http.html#hijacking-connections"><code>nng_http_hijack</code></a>.
+They can be used to transfer request or response body data as well.</p>
+<h3 id="hijacking-connections"><a class="header" href="#hijacking-connections">Hijacking Connections</a></h3>
+<pre><code class="language-c">void nng_http_hijack(nng_http_conn *conn);
+</code></pre>
+<p>TODO: This API will change to convert the conn into a stream object.</p>
+<p>The <a name="a026"></a><code>nng_http_hijack</code> function hijacks the connection <em>conn</em>, causing it
+to be disassociated from the HTTP server where it was created.</p>
+<p>The purpose of this function is the creation of HTTP upgraders (such as
+WebSocket), where the underlying HTTP connection will be taken over for
+some other purpose, and should not be used any further by the server.</p>
+<p>This function is most useful when called from a handler function.
+(See [<code>nng_http_handler_alloc</code>].)</p>
+<div class="mdbook-alerts mdbook-alerts-note">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ note
+</p>
+<p>It is the responsibility of the caller to dispose of the underlying connection when it is no longer needed.
+Furthermore, the HTTP server will no longer send any responses to the hijacked connection, so the caller should do that as well if appropriate.
+(See [<code>nng_http_write_response</code>].)</p>
+</div>
+<div class="mdbook-alerts mdbook-alerts-tip">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ tip
+</p>
+<p>This function is intended to facilitate uses cases that involve changing the protocol from HTTP, such as WebSocket.
+Most applications will never need to use this function.</p>
+</div>
+<h2 id="client-api"><a class="header" href="#client-api">Client API</a></h2>
+<p>The NNG client API consists of an API for creating connections, and an API for performing
+transactions on those connections.</p>
+<h3 id="client-object"><a class="header" href="#client-object">Client Object</a></h3>
+<pre><code class="language-c">typedef struct nng_http_client nng_http_client;
+</code></pre>
+<p>The <a name="a027"></a><code>nng_http_client</code> object is the client side creator for <a href="/api/http.html#connection-object"><code>nng_http</code></a> objects.
+It is analogous to a <a href="/TODO.html">dialer</a> object used elsewhere in NNG, but it specifically is only for HTTP.</p>
+<h3 id="create-a-client"><a class="header" href="#create-a-client">Create a Client</a></h3>
+<pre><code class="language-c">void nng_http_client_alloc(nng_http_client *clientp, const nng_url *url);
+</code></pre>
+<p>The <a name="a028"></a><code>nng_http_client_alloc</code> allocates an HTTP client suitable for
+connecting to the server identified by <em>url</em> and stores a pointer to
+it in the location referenced by <em>clientp</em>.</p>
+<h3 id="destroy-a-client"><a class="header" href="#destroy-a-client">Destroy a Client</a></h3>
+<pre><code class="language-c">void nng_http_client_free(nng_http_client *client);
+</code></pre>
+<p>The <a name="a029"></a><code>nng_http_client_free</code> connection destroys the client object and any
+of its resources.</p>
+<div class="mdbook-alerts mdbook-alerts-note">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ note
+</p>
+<p>Any connections created by <a href="/api/http.html#creating-connections"><code>nng_http_client_connect</code></a> are not affected by this function,
+and must be closed explicitly as needed.</p>
+</div>
+<h3 id="client-tls"><a class="header" href="#client-tls">Client TLS</a></h3>
+<pre><code class="language-c">int nng_http_client_get_tls(nng_http_client *client, nng_tls_config **tlsp);
+int nng_http_client_set_tls(nng_http_client *client, nng_tls_config *tls);
+</code></pre>
+<p>The <a name="a030"></a><code>nng_http_client_get_tls</code> and <a name="a031"></a><code>nng_http_client_set_tls</code> functions are used to
+retrieve or change the <a href="/TODO.html">TLS configuration</a> used when making outbound connections, enabling
+<a name="a032"></a>TLS as a result.</p>
+<p>If TLS has not been previously configured on <em>client</em>, then <code>nng_http_client_get_tls</code> will return <a href="/api/errors.html#NNG_EINVAL"><code>NNG_EINVAL</code></a>.
+Both functions will return <a href="/api/errors.html#NNG_ENOTSUP"><code>NNG_ENOTSUP</code></a> if either HTTP or TLS is not supported.</p>
+<p>Calling <code>nng_http_client_set_tls</code> invalidates any client previously obtained with
+<code>nng_http_client_get_tls</code>, unless a separate hold on the object was obtained.</p>
+<p>Once TLS is enabled for an <code>nng_http_client</code>, it is not possible to disable TLS.</p>
+<div class="mdbook-alerts mdbook-alerts-note">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ note
+</p>
+<p>The TLS configuration itself cannnot be changed once it has been used to create a connection,
+such as by calling <a href="/api/http.html#creating-connections"><code>nng_http_client_connect</code></a>, but a new one can be installed in the client.
+Existing connections will use the TLS configuration that there were created with.</p>
+</div>
+<h3 id="creating-connections"><a class="header" href="#creating-connections">Creating Connections</a></h3>
+<pre><code class="language-c">#include &lt;nng/http.h&gt;
+
+void nng_http_client_connect(nng_http_client *client, nng_aio *aio);
+</code></pre>
+<p>The <a name="a033"></a><code>nng_http_client_connect</code> function makes an outgoing connection to the
+server configured for <em>client</em>, and creates an <a href="/api/http.html#connection-object"><code>nng_http</code></a> object for the connection.</p>
+<p>This is done asynchronously, and when the operation succeseds the connection may be
+retried from the <em>aio</em> using <a href="/api/aio.html#inputs-and-outputs"><code>nng_aio_get_output</code></a> with index 0.</p>
+<h4 id="example-1-connecting-to-google"><a class="header" href="#example-1-connecting-to-google">Example 1: Connecting to Google</a></h4>
+<pre><code class="language-c">nng_aio *aio;
+nng_url *url;
+nng_http_client *client;
+nng_http *conn;
+int rv;
+
+// Error checks elided for clarity.
+nng_url_parse(&amp;url, "http://www.google.com");
+nng_aio_alloc(&amp;aio, NULL, NULL);
+nng_http_client_alloc(&amp;client, url);
+
+nng_http_client_connect(client, aio);
+
+// Wait for connection to establish (or attempt to fail).
+nng_aio_wait(aio);
+
+if ((rv = nng_aio_result(aio)) != 0) {
+ printf("Connection failed: %s\n", nng_strerror(rv));
+} else {
+ // Connection established, get it.
+ conn = nng_aio_get_output(aio, 0);
+
+ // ... do something with it here
+
+ // Close the connection when done to avoid leaking it.
+ nng_http_close(conn);
+}
+</code></pre>
+<h3 id="preparing-a-transaction"><a class="header" href="#preparing-a-transaction">Preparing a Transaction</a></h3>
+<pre><code class="language-c">int nng_http_set_version(nng_http *conn, const char *version);
+int nng_http_set_uri(nng_http *conn, const char *uri);
+</code></pre>
+<p>The <a name="a034"></a><code>nng_http_set_uri</code> function provides a URI for the transaction. This will be used to
+set the URI for the request. The URI typically appears like a path, starting with “/”, although
+it may also contain a query string.</p>
+<h3 id="request-body"><a class="header" href="#request-body">Request Body</a></h3>
+<h3 id="sending-the-request"><a class="header" href="#sending-the-request">Sending the Request</a></h3>
+<pre><code class="language-c">void nng_http_write_request(nng_http *conn, nng_aio *aio);
+</code></pre>
+<p>The <a name="a035"></a><code>nng_http_write_request</code> function starts an asynchronous write of
+the HTTP request associated with <em>conn</em>.
+The entire request is sent,
+including headers, and if present, the request body data.
+(The request body can be set with
+[<code>nng_http_set_data</code>] or [<code>nng_http_copy_data</code>].)</p>
+<p>This function returns immediately, with no return value.
+Completion of the operation is signaled via the <em>aio</em>, and the final result
+may be obtained via <a href="/api/aio.html#result-of-operation"><code>nng_aio_result</code></a>.</p>
+<div class="mdbook-alerts mdbook-alerts-tip">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ tip
+</p>
+<p>Consider using the [<code>nng_http_transact</code>] function,
+which provides a simpler interface for performing a complete HTTP client transaction.</p>
+</div>
+<h2 id="obtaining-the-response"><a class="header" href="#obtaining-the-response">Obtaining the Response</a></h2>
+<pre><code class="language-c">void nng_http_read_response(nng_http *conn, nng_aio *aio);
+</code></pre>
+<p>The <a name="a036"></a><code>nng_http_read_response</code> function starts an asynchronous read from the
+HTTP connection <em>conn</em>, reading an HTTP response into the response associated with <em>conn</em>, including all
+of the related headers.</p>
+<p>It does <em>not</em> transfer any response body. To do that, use <a href="/api/http.html#direct-read-and-write"><code>nng_http_read_all</code></a> or <a href="/api/http.html#direct-read-and-write"><code>nng_http_read</code></a>.</p>
+<div class="mdbook-alerts mdbook-alerts-note">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ note
+</p>
+<p>At this time we have no API support for reading chunked transfers directly. Applications that
+need to do so may use the direct read functions.</p>
+</div>
+<div class="mdbook-alerts mdbook-alerts-tip">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ tip
+</p>
+<p>An easier one-shot method for many use cases might be [<code>nng_http_transact</code>].</p>
+</div>
+<h3 id="submitting-the-transaction"><a class="header" href="#submitting-the-transaction">Submitting the Transaction</a></h3>
+<pre><code class="language-c">int nng_http_transact(nng_http *conn, nng_aio *aio);
+</code></pre>
+<p>The HTTP request is issued, and the response processed, asynchronously by the <a name="a037"></a><code>nng_http_transact</code> function.
+When the function is complete, the <em>aio</em> will be notified.</p>
+<p>The <a name="a038"></a><code>nng_http_transact</code> function is used to perform a complete
+HTTP exchange over the connection <em>conn</em>, sending the request
+and attached body data to the remote server, and reading the response.</p>
+<p>The entire response is read, including any associated body, which can
+subsequently be obtained using [<code>nng_http_get_data</code>].</p>
+<p>This function is intended to make creation of client applications easier,
+by performing multiple asynchronous operations required to complete an
+entire HTTP transaction.</p>
+<p>If an error occurs, the caller should close <em>conn</em> with <a href="/api/http.html#closing-the-connection"><code>nng_http_close</code></a>, as it may not
+necessarily be usable with other transactions.</p>
+<div class="mdbook-alerts mdbook-alerts-warning">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ warning
+</p>
+<p>If the remote server tries to send an extremely large buffer,
+then a corresponding allocation will be made, which can lead to denial
+of service attacks.
+Client applications should take care to use this only with reasonably
+trust-worthy servers.</p>
+</div>
+<div class="mdbook-alerts mdbook-alerts-note">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ note
+</p>
+<p>A given connection <em>conn</em> should be used with only one
+operation or transaction at a time as HTTP/1.1 has no support for
+request interleaving.</p>
+</div>
+<p>This function returns immediately, with no return value.
+Completion of the operation is signaled via the <em>aio</em>, and the final result
+may be obtained via [<code>nng_aio_result()</code>].</p>
+<h3 id="response-body"><a class="header" href="#response-body">Response Body</a></h3>
+<h2 id="server-api"><a class="header" href="#server-api">Server API</a></h2>
+<h3 id="handlers"><a class="header" href="#handlers">Handlers</a></h3>
+<h3 id="sending-the-response"><a class="header" href="#sending-the-response">Sending the Response</a></h3>
+<pre><code class="language-c">void nng_http_write_response(nng_http *conn, nng_aio *aio);
+</code></pre>
+<p>Normally the server will send any attached response, but there are circumstances where
+a response must be sent manually, such as when <a href="/api/http.html#hijacking-connections">hijacking</a> a connection.</p>
+<p>In such a case, <a name="a039"></a><code>nng_http_write_response</code> can be called, which will send the response and any attached data, asynchronously
+using the <a href="/api/aio.html#asynchronous-io-handle"><code>nng_aio</code></a> <em>aio</em>.</p>
+<p>By default, for <code>HTTP/1.1</code> connections, the connection is kept open, and
+will be reused to receive new requests. For <code>HTTP/1.0</code>, or if the client has requested
+explicitly by setting the “Connection: close” header, the connection will be closed after the
+response is fully sent.</p>
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