Skip to content

vllm.parser.utils

Functions:

extract_json_member_object(raw, key)

Extract the raw text span of the top-level object-valued member key from a (possibly incomplete) {...} JSON wrapper.

Returns the verbatim substring (prefix-stable as the input grows, which the engine's argument-delta diffing relies on), possibly an unterminated object prefix; None when the value has not started. Raises ValueError when the member is present but its value is not a JSON object. A verbatim substring (not re-serialized JSON) is required because the engine diffs successive converter outputs and expects each to extend the previous one; the scanner is string/escape-aware so a matching literal inside another value cannot mislead it, and it recovers a partial span when the wrapper is truncated (where json.loads would fail).

Source code in vllm/parser/utils.py 
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
def extract_json_member_object(raw: str, key: str) -> str | None:
    """Extract the raw text span of the top-level object-valued member ``key``
    from a (possibly incomplete) ``{...}`` JSON wrapper.

    Returns the verbatim substring (prefix-stable as the input grows, which
    the engine's argument-delta diffing relies on), possibly an unterminated
    object prefix; ``None`` when the value has not started. Raises
    ``ValueError`` when the member is present but its value is not a JSON
    object. A verbatim substring (not re-serialized JSON) is required because
    the engine diffs successive converter outputs and expects each to extend
    the previous one; the scanner is string/escape-aware so a matching literal
    inside another value cannot mislead it, and it recovers a partial span when
    the wrapper is truncated (where ``json.loads`` would fail)."""
    depth = 0
    in_string = False
    escape = False
    string_start = -1
    last_string: str | None = None
    for i, ch in enumerate(raw):
        if escape:
            escape = False
            continue
        if in_string:
            if ch == "\\":
                escape = True
            elif ch == '"':
                in_string = False
                if depth == 1:
                    last_string = raw[string_start + 1 : i]
            continue
        if ch == '"':
            in_string = True
            string_start = i
        elif ch == ":" and depth == 1 and last_string == key:
            value_start = i + 1
            while value_start < len(raw) and raw[value_start] in _JSON_WS:
                value_start += 1
            if value_start >= len(raw):
                return None
            if raw[value_start] != "{":
                raise ValueError(f"member {key!r} must be a JSON object")
            value_end = scan_json_object_end(raw, value_start)
            if value_end is None:
                return raw[value_start:]
            return raw[value_start:value_end]
        elif ch in "{[":
            depth += 1
        elif ch in "}]":
            depth -= 1
    return None

scan_json_object_end(raw, start)

Return the end index (exclusive) of the JSON object starting at raw[start] (which must be {), or None when it is still unterminated. String- and escape-aware so braces inside strings do not mislead the depth count.

Source code in vllm/parser/utils.py 
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
def scan_json_object_end(raw: str, start: int) -> int | None:
    """Return the end index (exclusive) of the JSON object starting at
    ``raw[start]`` (which must be ``{``), or ``None`` when it is still
    unterminated. String- and escape-aware so braces inside strings do not
    mislead the depth count."""
    depth = 0
    in_string = False
    escape = False
    for i in range(start, len(raw)):
        ch = raw[i]
        if escape:
            escape = False
            continue
        if in_string:
            if ch == "\\":
                escape = True
            elif ch == '"':
                in_string = False
            continue
        if ch == '"':
            in_string = True
        elif ch == "{":
            depth += 1
        elif ch == "}":
            depth -= 1
            if depth == 0:
                return i + 1
    return None