2.1.1.6 LengthPrefixedString
The LengthPrefixedString represents a string value. The string is prefixed by the length of the UTF-8 encoded string in bytes. The length is encoded in a variable-length field with a minimum of 1 byte and a maximum of 5 bytes. To minimize the wire size, length is encoded as a variable-length field.
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Length (variable) |
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String (variable) |
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Length (variable): A numerical value that can range from 0 to 2147483647 (2^31) inclusive.
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To minimize the wire size, the encoding of the length MUST be encoded as follows:
The Length field MUST be at least 1 byte and MUST NOT be more than 5 bytes.
Each byte MUST hold the Length value in its lower 7 bits.
The high bit MUST be used to indicate that the length continues in the next byte.
In the case that all 5 bytes are used, the high 5 bits in the fifth byte MUST be 0.
0
1
2
3
4
5
6
7
8
91
0
1
2
3
4
5
6
7
8
92
0
1
2
3
4
5
6
7
8
93
0
1Length_0-6
A
-
Length_0-6 (7 bits): Length values range from 0 to 127 (7 bits).
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A - Reserved_7 (1 bit): The value MUST be 0.
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0
1
2
3
4
5
6
7
8
91
0
1
2
3
4
5
6
7
8
92
0
1
2
3
4
5
6
7
8
93
0
1Length_0-6
A
Length_8-14
B
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Length_0-6 (7 bits): Length values range from 128 to 16383 (14 bits).
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A - Reserved_7 (1 bit): The value MUST be 1.
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Length_8-14 (7 bits): Length values range from 128 to 16383 (14 bits).
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B - Reserved_15 (1 bit): The value MUST be 0.
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0
1
2
3
4
5
6
7
8
91
0
1
2
3
4
5
6
7
8
92
0
1
2
3
4
5
6
7
8
93
0
1Length_0-6
A
Length_8-14
B
Length_16-22
C
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Length_0-6 (7 bits): Length values range from 16384 to 2097151 (21 bits).
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A - Reserved_7 (1 bit): The value MUST be 1.
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Length_8-14 (7 bits): Length values range from 16384 to 2097151 (21 bits).
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B - Reserved_15 (1 bit): The value MUST be 1.
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Length_16-22 (7 bits): Length values range from 16384 to 2097151 (21 bits).
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C - Reserved_23 (1 bit): The value MUST be 0.
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0
1
2
3
4
5
6
7
8
91
0
1
2
3
4
5
6
7
8
92
0
1
2
3
4
5
6
7
8
93
0
1Length_0-6
A
Length_8-14
B
Length_16-22
C
Length_24-30
D
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Length_0-6 (7 bits): Length values range from 2097152 to 268435445 (28 bits).
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A - Reserved_7 (1 bit): The value MUST be 1.
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Length_8-14 (7 bits): Length values range from 2097152 to 268435445 (28 bits).
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B - Reserved_15 (1 bit): The value MUST be 1.
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Length_16-22 (7 bits): Length values range from 2097152 to 268435445 (28 bits).
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C - Reserved_23 (1 bit): The value MUST be 1.
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Length_24-30 (7 bits): Length values range from 2097152 to 268435445 (28 bits).
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D - Reserved_31 (1 bit): The value MUST be 0.
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0
1
2
3
4
5
6
7
8
91
0
1
2
3
4
5
6
7
8
92
0
1
2
3
4
5
6
7
8
93
0
1Length_0-6
A
Length_8-14
B
Length_16-22
C
Length_24-30
D
Length_32-38
E
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Length_0-6 (7 bits): Length values range from 268435456 to 2147483647 (31 bits).
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A - Reserved_7 (1 bit): The value MUST be 1.
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Length_8-14 (7 bits): Length values range from 268435456 to 2147483647 (31 bits).
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B - Reserved_15 (1 bit): The value MUST be 1.
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Length_16-22 (7 bits): Length values range from 268435456 to 2147483647 (31 bits).
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C - Reserved_23 (1 bit): The value MUST be 1.
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Length_24-30 (7 bits): Length values range from 268435456 to 2147483647 (31 bits).
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D - Reserved_31 (1 bit): The value MUST be 1.
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Length_32-38 (7 bits): Length values range from 268435456 to 2147483647 (31 bits).
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E - Reserved_39 (1 bit): The value MUST be 0.
String (variable): A UTF-8 encoded string value. The number of bytes of the encoded string MUST be equal to the value specified in the Length field.