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Key English Actions
Chunked Encoding
For message payloads whose size is not known ahead of time, HTTP version 1.1 defines the [@https://tools.ietf.org/html/rfc7230#section-4.1 ['chunked]] transfer coding. This coding consists of zero or more [@https://tools.ietf.org/html/rfc7230#section-4.1 ['chunked bodies]], followed by a [@https://tools.ietf.org/html/rfc7230#section-4.1 ['last chunk]]. Each chunked body may contain optional application-defined, connection-specific [@https://tools.ietf.org/html/rfc7230#section-4.1.1 ['chunk-extensions]]. The last chunk may contain additional HTTP field values in a section of the last chunk called a [@https://tools.ietf.org/html/rfc7230#section-4.1.2 ['chunk-trailer]]. The field values are "promised" in the header as a comma delimited list of field names in the [@https://tools.ietf.org/html/rfc7230#section-4.4 [*Trailer]] field value. Clients indicate their willingness to accept trailers by including the "trailers" token in the [@https://tools.ietf.org/html/rfc7230#section-4.3 [*TE]] field value.
Serializing Chunks
The __serializer__ automatically applies the chunked transfer encoding when a message returns `true` from [link beast.ref.boost__beast__http__message.chunked.overload1 `message::chunked`]. The boundaries between chunks emitted by the serializer are implementation defined. Chunk extensions and trailers are omitted. Applications which need precise control over the chunk boundaries, extensions, and trailers may use a set of helper classes which enable manual emission of message payloads using chunk encoding.
To use these helper classes, first serialize the header portion of the message using the standard interface. Then prepare the buffers, chunk extensions, and desired trailers, and use them with these helpers:
Chunking Helpers
47
Name
47
Description
[link beast.ref.boost__beast__http__chunk_body `chunk_body`]
A buffer sequence representing a complete chunk body.
[link beast.ref.boost__beast__http__chunk_crlf `chunk_crlf`]
A buffer sequence representing the CRLF (`"\r\n"`) delimiter. This class is used when the caller desires to emit the chunk body in two or more individual stream operations.
[link beast.ref.boost__beast__http__chunk_extensions `chunk_extensions`]

[link beast.ref.boost__beast__http__basic_chunk_extensions `basic_chunk_extensions`]
This is a simple, allocating container which lets callers easily build up a set of chunk extensions.
[link beast.ref.boost__beast__http__chunk_header `chunk_header`]
A buffer sequence representing a hex-encoded chunk size, followed by an optional set of chunk extensions, including the terminating CRLF (`"\r\n"`) delimiter which precedes the chunk body. This class is used when the caller desires to emit the chunk body in two or more individual stream operations.
[link beast.ref.boost__beast__http__chunk_last `chunk_last`]
A buffer sequence representing a last chunk. The last chunk indicates the end of the chunked message payload, and may contain optional trailer fields.
[link beast.ref.boost__beast__http__make_chunk `make_chunk`]

[link beast.ref.boost__beast__http__make_chunk_last `make_chunk_last`]
These helper functions are used to construct a chunk or last chunk directly at call sites.
We demonstrate the use of these objects first by declaring a function which returns the next buffer sequence to use as a chunk body:
This example demonstrates sending a complete chunked message payload manually. No chunk extensions or trailers are emitted:
The following code sends additional chunks, and sets chunk extensions using the helper container. The container automatically quotes values in the serialized output when necessary:
Callers can take over the generation and management of the extensions buffer by passing a non-owning string. Note that this requires the string contents to adhere to the correct syntax for chunk extensions, including the needed double quotes for values which contain spaces:
The next code sample emits a chunked response which promises two trailer fields and delivers them in the last chunk. The implementation allocates memory using the default or a passed-in allocator to hold the state information required to serialize the trailer:
Using a custom allocator to serialize the last chunk:
Alternatively, callers can take over the generation and lifetime management of the serialized trailer fields by passing in a non-owning string:
For the ultimate level of control, a caller can manually compose the chunk itself by first emitting a header with the correct chunk body size, and then by emitting the chunk body in multiple calls to the stream write function. In this case the caller is responsible for also emitting the terminating CRLF (`"\r\n"`):
English Actions
Chunked Encoding
For message payloads whose size is not known ahead of time, HTTP version 1.1 defines the [@https://tools.ietf.org/html/rfc7230#section-4.1 ['chunked]] transfer coding. This coding consists of zero or more [@https://tools.ietf.org/html/rfc7230#section-4.1 ['chunked bodies]], followed by a [@https://tools.ietf.org/html/rfc7230#section-4.1 ['last chunk]]. Each chunked body may contain optional application-defined, connection-specific [@https://tools.ietf.org/html/rfc7230#section-4.1.1 ['chunk-extensions]]. The last chunk may contain additional HTTP field values in a section of the last chunk called a [@https://tools.ietf.org/html/rfc7230#section-4.1.2 ['chunk-trailer]]. The field values are "promised" in the header as a comma delimited list of field names in the [@https://tools.ietf.org/html/rfc7230#section-4.4 [*Trailer]] field value. Clients indicate their willingness to accept trailers by including the "trailers" token in the [@https://tools.ietf.org/html/rfc7230#section-4.3 [*TE]] field value.
Serializing Chunks
The __serializer__ automatically applies the chunked transfer encoding when a message returns `true` from [link beast.ref.boost__beast__http__message.chunked.overload1 `message::chunked`]. The boundaries between chunks emitted by the serializer are implementation defined. Chunk extensions and trailers are omitted. Applications which need precise control over the chunk boundaries, extensions, and trailers may use a set of helper classes which enable manual emission of message payloads using chunk encoding.
To use these helper classes, first serialize the header portion of the message using the standard interface. Then prepare the buffers, chunk extensions, and desired trailers, and use them with these helpers:
Chunking Helpers
[link beast.ref.boost__beast__http__chunk_body `chunk_body`]
A buffer sequence representing a complete chunk body.
[link beast.ref.boost__beast__http__chunk_crlf `chunk_crlf`]
A buffer sequence representing the CRLF (`"\r\n"`) delimiter. This class is used when the caller desires to emit the chunk body in two or more individual stream operations.
[link beast.ref.boost__beast__http__chunk_extensions `chunk_extensions`]

[link beast.ref.boost__beast__http__basic_chunk_extensions `basic_chunk_extensions`]
This is a simple, allocating container which lets callers easily build up a set of chunk extensions.
[link beast.ref.boost__beast__http__chunk_header `chunk_header`]
A buffer sequence representing a hex-encoded chunk size, followed by an optional set of chunk extensions, including the terminating CRLF (`"\r\n"`) delimiter which precedes the chunk body. This class is used when the caller desires to emit the chunk body in two or more individual stream operations.
[link beast.ref.boost__beast__http__chunk_last `chunk_last`]
A buffer sequence representing a last chunk. The last chunk indicates the end of the chunked message payload, and may contain optional trailer fields.
[link beast.ref.boost__beast__http__make_chunk `make_chunk`]

[link beast.ref.boost__beast__http__make_chunk_last `make_chunk_last`]
These helper functions are used to construct a chunk or last chunk directly at call sites.
We demonstrate the use of these objects first by declaring a function which returns the next buffer sequence to use as a chunk body:
This example demonstrates sending a complete chunked message payload manually. No chunk extensions or trailers are emitted:
The following code sends additional chunks, and sets chunk extensions using the helper container. The container automatically quotes values in the serialized output when necessary:
Callers can take over the generation and management of the extensions buffer by passing a non-owning string. Note that this requires the string contents to adhere to the correct syntax for chunk extensions, including the needed double quotes for values which contain spaces:
The next code sample emits a chunked response which promises two trailer fields and delivers them in the last chunk. The implementation allocates memory using the default or a passed-in allocator to hold the state information required to serialize the trailer:
Using a custom allocator to serialize the last chunk:
Alternatively, callers can take over the generation and lifetime management of the serialized trailer fields by passing in a non-owning string:
Input
Output
HTTP/1.1 200 OK\r\n
Server: test\r\n
Trailer: Expires, Content-MD5\r\n
Transfer-Encoding: chunked\r\n
\r\n
5\r\n
First\r\n
d;quality=1.0\r\n
Hello, world!\r\n
e;file=abc.txt;quality=0.7\r\n
The Next Chunk\r\n
8;last\r\n
Last one\r\n
0\r\n
Expires: never\r\n
Content-MD5: f4a5c16584f03d90\r\n
\r\n
Chunk Body: First
Extension: quality = 1.0
Chunk Body: Hello, world!
Extension: file = abc.txt
Extension: quality = 0.7
Chunk Body: The Next Chunk
Extension: last
Chunk Body: Last one
Expires: never
Content-MD5: f4a5c16584f03d90

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String added in the repository
[link beast.ref.boost__beast__http__chunk_extensions `chunk_extensions`]

[link beast.ref.boost__beast__http__basic_chunk_extensions `basic_chunk_extensions`]
[link beast.ref.boost__beast__http__chunk_extensions `chunk_extensions`]

[link beast.ref.boost__beast__http__basic_chunk_extensions `basic_chunk_extensions`]
06/05/2026
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String information

Component
Boost Beast Translation (zh_Hans)/Doc / Qbk / 04 Http / 08 Chunked Encoding (qbk)
Source string description
type: table cell
Flags
read-only
Unit identifier
57386
Source string location
string ID 47
String age
06/05/2026
Last updated
06/05/2026
Source string age
06/05/2026
Translation file QuickBook file
doc/qbk/04_http/08_chunked_encoding.qbk, string 13