-;; Incremental JSON parsing
-
-(defun notmuch-json-create-parser (buffer)
- "Return a streaming JSON parser that consumes input from BUFFER.
-
-This parser is designed to read streaming JSON whose structure is
-known to the caller. Like a typical JSON parsing interface, it
-provides a function to read a complete JSON value from the input.
-However, it extends this with an additional function that
-requires the next value in the input to be a compound value and
-descends into it, allowing its elements to be read one at a time
-or further descended into. Both functions can return 'retry to
-indicate that not enough input is available.
-
-The parser always consumes input from BUFFER's point. Hence, the
-caller is allowed to delete and data before point and may
-resynchronize after an error by moving point."
-
- (list buffer
- ;; Terminator stack: a stack of characters that indicate the
- ;; end of the compound values enclosing point
- '()
- ;; Next: One of
- ;; * 'expect-value if the next token must be a value, but a
- ;; value has not yet been reached
- ;; * 'value if point is at the beginning of a value
- ;; * 'expect-comma if the next token must be a comma
- 'expect-value
- ;; Allow terminator: non-nil if the next token may be a
- ;; terminator
- nil
- ;; Partial parse position: If state is 'value, a marker for
- ;; the position of the partial parser or nil if no partial
- ;; parsing has happened yet
- nil
- ;; Partial parse state: If state is 'value, the current
- ;; `parse-partial-sexp' state
- nil))
-
-(defmacro notmuch-json-buffer (jp) `(first ,jp))
-(defmacro notmuch-json-term-stack (jp) `(second ,jp))
-(defmacro notmuch-json-next (jp) `(third ,jp))
-(defmacro notmuch-json-allow-term (jp) `(fourth ,jp))
-(defmacro notmuch-json-partial-pos (jp) `(fifth ,jp))
-(defmacro notmuch-json-partial-state (jp) `(sixth ,jp))
-
-(defvar notmuch-json-syntax-table
- (let ((table (make-syntax-table)))
- ;; The standard syntax table is what we need except that "." needs
- ;; to have word syntax instead of punctuation syntax.
- (modify-syntax-entry ?. "w" table)
- table)
- "Syntax table used for incremental JSON parsing.")
-
-(defun notmuch-json-scan-to-value (jp)
- ;; Helper function that consumes separators, terminators, and
- ;; whitespace from point. Returns nil if it successfully reached
- ;; the beginning of a value, 'end if it consumed a terminator, or
- ;; 'retry if not enough input was available to reach a value. Upon
- ;; nil return, (notmuch-json-next jp) is always 'value.
-
- (if (eq (notmuch-json-next jp) 'value)
- ;; We're already at a value
- nil
- ;; Drive the state toward 'expect-value
- (skip-chars-forward " \t\r\n")
- (or (when (eobp) 'retry)
- ;; Test for the terminator for the current compound
- (when (and (notmuch-json-allow-term jp)
- (eq (char-after) (car (notmuch-json-term-stack jp))))
- ;; Consume it and expect a comma or terminator next
- (forward-char)
- (setf (notmuch-json-term-stack jp) (cdr (notmuch-json-term-stack jp))
- (notmuch-json-next jp) 'expect-comma
- (notmuch-json-allow-term jp) t)
- 'end)
- ;; Test for a separator
- (when (eq (notmuch-json-next jp) 'expect-comma)
- (when (/= (char-after) ?,)
- (signal 'json-readtable-error (list "expected ','")))
- ;; Consume it, switch to 'expect-value, and disallow a
- ;; terminator
- (forward-char)
- (skip-chars-forward " \t\r\n")
- (setf (notmuch-json-next jp) 'expect-value
- (notmuch-json-allow-term jp) nil)
- ;; We moved point, so test for eobp again and fall through
- ;; to the next test if there's more input
- (when (eobp) 'retry))
- ;; Next must be 'expect-value and we know this isn't
- ;; whitespace, EOB, or a terminator, so point must be on a
- ;; value
- (progn
- (assert (eq (notmuch-json-next jp) 'expect-value))
- (setf (notmuch-json-next jp) 'value)
- nil))))
-
-(defun notmuch-json-begin-compound (jp)
- "Parse the beginning of a compound value and traverse inside it.
-
-Returns 'retry if there is insufficient input to parse the
-beginning of the compound. If this is able to parse the
-beginning of a compound, it moves point past the token that opens
-the compound and returns t. Later calls to `notmuch-json-read'
-will return the compound's elements.
-
-Entering JSON objects is currently unimplemented."
-
- (with-current-buffer (notmuch-json-buffer jp)
- ;; Disallow terminators
- (setf (notmuch-json-allow-term jp) nil)
- (or (notmuch-json-scan-to-value jp)
- (if (/= (char-after) ?\[)
- (signal 'json-readtable-error (list "expected '['"))
- (forward-char)
- (push ?\] (notmuch-json-term-stack jp))
- ;; Expect a value or terminator next
- (setf (notmuch-json-next jp) 'expect-value
- (notmuch-json-allow-term jp) t)
- t))))
-
-(defun notmuch-json-read (jp)
- "Parse the value at point in JP's buffer.
-
-Returns 'retry if there is insufficient input to parse a complete
-JSON value (though it may still move point over separators or
-whitespace). If the parser is currently inside a compound value
-and the next token ends the list or object, this moves point just
-past the terminator and returns 'end. Otherwise, this moves
-point to just past the end of the value and returns the value."
-
- (with-current-buffer (notmuch-json-buffer jp)
- (or
- ;; Get to a value state
- (notmuch-json-scan-to-value jp)
-
- ;; Can we parse a complete value?
- (let ((complete
- (if (looking-at "[-+0-9tfn]")
- ;; This is a number or a keyword, so the partial
- ;; parser isn't going to help us because a truncated
- ;; number or keyword looks like a complete symbol to
- ;; it. Look for something that clearly ends it.
- (save-excursion
- (skip-chars-forward "^]},: \t\r\n")
- (not (eobp)))
-
- ;; We're looking at a string, object, or array, which we
- ;; can partial parse. If we just reached the value, set
- ;; up the partial parser.
- (when (null (notmuch-json-partial-state jp))
- (setf (notmuch-json-partial-pos jp) (point-marker)))
-
- ;; Extend the partial parse until we either reach EOB or
- ;; get the whole value
- (save-excursion
- (let ((pstate
- (with-syntax-table notmuch-json-syntax-table
- (parse-partial-sexp
- (notmuch-json-partial-pos jp) (point-max) 0 nil
- (notmuch-json-partial-state jp)))))
- ;; A complete value is available if we've reached
- ;; depth 0 or less and encountered a complete
- ;; subexpression.
- (if (and (<= (first pstate) 0) (third pstate))
- t
- ;; Not complete. Update the partial parser state
- (setf (notmuch-json-partial-pos jp) (point-marker)
- (notmuch-json-partial-state jp) pstate)
- nil))))))
-
- (if (not complete)
- 'retry
- ;; We have a value. Reset the partial parse state and expect
- ;; a comma or terminator after the value.
- (setf (notmuch-json-next jp) 'expect-comma
- (notmuch-json-allow-term jp) t
- (notmuch-json-partial-pos jp) nil
- (notmuch-json-partial-state jp) nil)
- ;; Parse the value
- (let ((json-object-type 'plist)
- (json-array-type 'list)
- (json-false nil))
- (json-read)))))))
-
-(defun notmuch-json-eof (jp)
- "Signal a json-error if there is more data in JP's buffer.
-
-Moves point to the beginning of any trailing data or to the end
-of the buffer if there is only trailing whitespace."
-
- (with-current-buffer (notmuch-json-buffer jp)
- (skip-chars-forward " \t\r\n")
- (unless (eobp)
- (signal 'json-error (list "Trailing garbage following JSON data")))))
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