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+# nng_msg_body
+
+## NAME
+
+nng_msg_body --- message body
+
+## SYNOPSIS
+
+```c
+#include <nng/nng.h>
+
+void *nng_msg_body(nng_msg *msg);
+size_t nng_msg_len(nng_msg *msg);
+void nng_msg_clear(nng_msg *msg);
+int nng_msg_append(nng_msg *msg, const void *val, size_t size);
+int nng_msg_append_u16(nng_msg *msg, uint16_t val16);
+int nng_msg_append_u32(nng_msg *msg, uint32_t val32);
+int nng_msg_append_u64(nng_msg *msg, uint64_t val64);
+int nng_msg_insert(nng_msg *msg, const void *val, size_t size);
+int nng_msg_insert_u16(nng_msg *msg, uint16_t val16);
+int nng_msg_insert_u32(nng_msg *msg, uint32_t val32);
+int nng_msg_insert_u64(nng_msg *msg, uint64_t val64);
+int nng_msg_chop(nng_msg *msg, size_t size);
+int nng_msg_chop_u16(nng_msg *msg, uint16_t *val16);
+int nng_msg_chop_u32(nng_msg *msg, uint32_t *val32);
+int nng_msg_chop_u64(nng_msg *msg, uint64_t *val64);
+int nng_msg_trim(nng_msg *msg, size_t size);
+int nng_msg_trim_u16(nng_msg *msg, uint16_t *val16);
+int nng_msg_trim_u32(nng_msg *msg, uint32_t *val32);
+int nng_msg_trim_u64(nng_msg *msg, uint64_t *val64);
+```
+
+## DESCRIPTION
+
+The {{i:body}} of a message is the part of the message that is used
+for the application payload, and does not normally include protocol
+or transport-specific data.
+
+The `nng_msg_body` function returns a pointer to the start of the body
+content of the message _msg_.
+
+The `nng_msg_len` function returns the length of the message body in bytes.
+
+> [!IMPORTANT]
+> The value returned by `nng_msg_body` is invalidated by a call to any of the
+> functions that modify the message itself.
+
+The rest of these functions allow modifying the message body.
+
+### Clearing the Message Body
+
+The message body can be entirely cleared using {{i:`nng_msg_clear`}}.
+The underlying buffers are left intact, and the bytes may remain at their original values, so
+this function should not be relied upon for zeroizing sensitive data.
+
+### Appending and Inserting Data
+
+Appending data to a message body is done by using the {{i:`nng_msg_append`}} functions.
+The base `nng_msg_append` function appends _size_ bytes of untyped data to the end of the
+message.
+
+> [!TIP]
+> Using [`nng_msg_reserve`][nng_msg] to preallocate space before appending or inserting
+> can reduce allocations and data copies, for a significant performance benefit.
+
+Use of the typed versions, ending in suffixes `_u16`, `_u32`, and `_u64` allows
+for unsigned integers to be appended directly. The integers are encoded in network byte order, with
+the most significant byte appearing first. The message body will by two, four, or eight
+bytes accordingly.
+
+Data may inserted before the rest of the message body by using the {{i:`nng_msg_insert`}} functions.
+This will attempt to use "headroom" in the message to avoid a data copy.
+
+> [!TIP]
+> Message headroom is limited, so `nng_msg_insert` is best used sparingly.
+> It is much more efficient to build the message content from start to end
+> using `nng_msg_append`.
+
+Typed versions and the untyped base function behave similarly to the `nng_msg_append` functions.
+
+### Consuming Data
+
+The {{i:`nng_msg_trim`}} functions remove data from the beginning of the message body.
+This is accomplished by incrementing the pointer to start of the message by the appropriate size.
+
+Additionally, functions with typed suffixes (`_u16`, `_u32`, `_u64`) allow the data obtained to be decoded and returned.
+The data is assumed to have been in network byte order in the message, but is returned in
+the native machine byte order. The appropriate number of bytes is consumed for each of these types,
+so two bytes for `_u16`, four bytes for `_u32`, and eight bytes for `_u64`.
+
+The {{i:`nng_msg_chop`}} functions behave in a similar fashion, but consume data from the
+end of the message body.
+
+## RETURN VALUES
+
+The `nng_msg_body` function returns a pointer to the start of the message body.
+The `nng_msg_len` function returns the length of the message in bytes.
+The `nng_msg_clear` function does not return anything.
+The remaining functions return zero on success, or a non-zero error value on failure.
+
+## ERRORS
+
+- `NNG_ENOMEM`: Insufficient memory exists to grow the message.
+- `NNG_EINVAL`: The message body is too short to remove the requested data.
+
+## SEE ALSO
+
+[nng_msg][nng_msg],
+[nng_msg_header][nng_msg_header]
+
+[nng_msg]: ./nng_msg.md
+[nng_msg_header]: ./nng_msg_header.md