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+From: Austin Clements <amdragon@MIT.EDU>\r
+To: notmuch@notmuchmail.org\r
+Subject: [PATCH v2 7/9] emacs: Implement an incremental JSON parser\r
+Date: Thu, 5 Jul 2012 16:52:25 -0400\r
+Message-Id: <1341521547-15502-8-git-send-email-amdragon@mit.edu>\r
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+ <1341521547-15502-1-git-send-email-amdragon@mit.edu>\r
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+\r
+This parser is designed to read streaming JSON whose structure is\r
+known to the caller. Like a typical JSON parsing interface, it\r
+provides a function to read a complete JSON value from the input.\r
+However, it extends this with an additional function that\r
+requires the next value in the input to be a compound value and\r
+descends into it, allowing its elements to be read one at a time\r
+or further descended into. Both functions can return 'retry to\r
+indicate that not enough input is available.\r
+\r
+The parser supports efficient partial parsing, so there's no need to\r
+frame the input for correctness or performance.\r
+\r
+The bulk of the parsing is still done by Emacs' json.el, so any\r
+improvements or optimizations to that will benefit the incremental\r
+parser as well.\r
+\r
+Currently only descending into JSON lists is supported because that's\r
+all we need, but support for descending into JSON objects can be added\r
+in the future.\r
+---\r
+ emacs/notmuch-lib.el | 196 ++++++++++++++++++++++++++++++++++++++++++++++++++\r
+ 1 file changed, 196 insertions(+)\r
+\r
+diff --git a/emacs/notmuch-lib.el b/emacs/notmuch-lib.el\r
+index c829df3..9e04d97 100644\r
+--- a/emacs/notmuch-lib.el\r
++++ b/emacs/notmuch-lib.el\r
+@@ -23,6 +23,7 @@\r
+ \r
+ (require 'mm-view)\r
+ (require 'mm-decode)\r
++(require 'json)\r
+ (eval-when-compile (require 'cl))\r
+ \r
+ (defvar notmuch-command "notmuch"\r
+@@ -296,6 +297,201 @@ was called."\r
+ (defvar notmuch-show-process-crypto nil)\r
+ (make-variable-buffer-local 'notmuch-show-process-crypto)\r
+ \r
++;; Incremental JSON parsing\r
++\r
++(defun notmuch-json-create-parser (buffer)\r
++ "Return a streaming JSON parser that consumes input from BUFFER.\r
++\r
++This parser is designed to read streaming JSON whose structure is\r
++known to the caller. Like a typical JSON parsing interface, it\r
++provides a function to read a complete JSON value from the input.\r
++However, it extends this with an additional function that\r
++requires the next value in the input to be a compound value and\r
++descends into it, allowing its elements to be read one at a time\r
++or further descended into. Both functions can return 'retry to\r
++indicate that not enough input is available.\r
++\r
++The parser always consumes input from BUFFER's point. Hence, the\r
++caller is allowed to delete and data before point and may\r
++resynchronize after an error by moving point."\r
++\r
++ (list buffer\r
++ ;; Terminator stack: a stack of characters that indicate the\r
++ ;; end of the compound values enclosing point\r
++ '()\r
++ ;; Next: One of\r
++ ;; * 'expect-value if the next token must be a value, but a\r
++ ;; value has not yet been reached\r
++ ;; * 'value if point is at the beginning of a value\r
++ ;; * 'expect-comma if the next token must be a comma\r
++ 'expect-value\r
++ ;; Allow terminator: non-nil if the next token may be a\r
++ ;; terminator\r
++ nil\r
++ ;; Partial parse position: If state is 'value, a marker for\r
++ ;; the position of the partial parser or nil if no partial\r
++ ;; parsing has happened yet\r
++ nil\r
++ ;; Partial parse state: If state is 'value, the current\r
++ ;; `parse-partial-sexp' state\r
++ nil))\r
++\r
++(defmacro notmuch-json-buffer (jp) `(first ,jp))\r
++(defmacro notmuch-json-term-stack (jp) `(second ,jp))\r
++(defmacro notmuch-json-next (jp) `(third ,jp))\r
++(defmacro notmuch-json-allow-term (jp) `(fourth ,jp))\r
++(defmacro notmuch-json-partial-pos (jp) `(fifth ,jp))\r
++(defmacro notmuch-json-partial-state (jp) `(sixth ,jp))\r
++\r
++(defvar notmuch-json-syntax-table\r
++ (let ((table (make-syntax-table)))\r
++ ;; The standard syntax table is what we need except that "." needs\r
++ ;; to have word syntax instead of punctuation syntax.\r
++ (modify-syntax-entry ?. "w" table)\r
++ table)\r
++ "Syntax table used for incremental JSON parsing.")\r
++\r
++(defun notmuch-json-scan-to-value (jp)\r
++ ;; Helper function that consumes separators, terminators, and\r
++ ;; whitespace from point. Returns nil if it successfully reached\r
++ ;; the beginning of a value, 'end if it consumed a terminator, or\r
++ ;; 'retry if not enough input was available to reach a value. Upon\r
++ ;; nil return, (notmuch-json-next jp) is always 'value.\r
++\r
++ (if (eq (notmuch-json-next jp) 'value)\r
++ ;; We're already at a value\r
++ nil\r
++ ;; Drive the state toward 'expect-value\r
++ (skip-chars-forward " \t\r\n")\r
++ (or (when (eobp) 'retry)\r
++ ;; Test for the terminator for the current compound\r
++ (when (and (notmuch-json-allow-term jp)\r
++ (eq (char-after) (car (notmuch-json-term-stack jp))))\r
++ ;; Consume it and expect a comma or terminator next\r
++ (forward-char)\r
++ (setf (notmuch-json-term-stack jp) (cdr (notmuch-json-term-stack jp))\r
++ (notmuch-json-next jp) 'expect-comma\r
++ (notmuch-json-allow-term jp) t)\r
++ 'end)\r
++ ;; Test for a separator\r
++ (when (eq (notmuch-json-next jp) 'expect-comma)\r
++ (when (/= (char-after) ?,)\r
++ (signal 'json-readtable-error (list "expected ','")))\r
++ ;; Consume it, switch to 'expect-value, and disallow a\r
++ ;; terminator\r
++ (forward-char)\r
++ (skip-chars-forward " \t\r\n")\r
++ (setf (notmuch-json-next jp) 'expect-value\r
++ (notmuch-json-allow-term jp) nil)\r
++ ;; We moved point, so test for eobp again and fall through\r
++ ;; to the next test if there's more input\r
++ (when (eobp) 'retry))\r
++ ;; Next must be 'expect-value and we know this isn't\r
++ ;; whitespace, EOB, or a terminator, so point must be on a\r
++ ;; value\r
++ (progn\r
++ (assert (eq (notmuch-json-next jp) 'expect-value))\r
++ (setf (notmuch-json-next jp) 'value)\r
++ nil))))\r
++\r
++(defun notmuch-json-begin-compound (jp)\r
++ "Parse the beginning of a compound value and traverse inside it.\r
++\r
++Returns 'retry if there is insufficient input to parse the\r
++beginning of the compound. If this is able to parse the\r
++beginning of a compound, it moves point past the token that opens\r
++the compound and returns t. Later calls to `notmuch-json-read'\r
++will return the compound's elements.\r
++\r
++Entering JSON objects is current unimplemented."\r
++\r
++ (with-current-buffer (notmuch-json-buffer jp)\r
++ ;; Disallow terminators\r
++ (setf (notmuch-json-allow-term jp) nil)\r
++ (or (notmuch-json-scan-to-value jp)\r
++ (if (/= (char-after) ?\[)\r
++ (signal 'json-readtable-error (list "expected '['"))\r
++ (forward-char)\r
++ (push ?\] (notmuch-json-term-stack jp))\r
++ ;; Expect a value or terminator next\r
++ (setf (notmuch-json-next jp) 'expect-value\r
++ (notmuch-json-allow-term jp) t)\r
++ t))))\r
++\r
++(defun notmuch-json-read (jp)\r
++ "Parse the value at point in JP's buffer.\r
++\r
++Returns 'retry if there is insufficient input to parse a complete\r
++JSON value. If the parser is currently inside a compound value\r
++and the next token ends the list or object, returns 'end.\r
++Otherwise, moves point to just past the end of the value and\r
++returns the value."\r
++\r
++ (with-current-buffer (notmuch-json-buffer jp)\r
++ (or\r
++ ;; Get to a value state\r
++ (notmuch-json-scan-to-value jp)\r
++\r
++ ;; Can we parse a complete value?\r
++ (let ((complete\r
++ (if (looking-at "[-+0-9tfn]")\r
++ ;; This is a number or a keyword, so the partial\r
++ ;; parser isn't going to help us because a truncated\r
++ ;; number or keyword looks like a complete symbol to\r
++ ;; it. Look for something that clearly ends it.\r
++ (save-excursion\r
++ (skip-chars-forward "^]},: \t\r\n")\r
++ (not (eobp)))\r
++\r
++ ;; We're looking at a string, object, or array, which we\r
++ ;; can partial parse. If we just reached the value, set\r
++ ;; up the partial parser.\r
++ (when (null (notmuch-json-partial-state jp))\r
++ (setf (notmuch-json-partial-pos jp) (point-marker)))\r
++\r
++ ;; Extend the partial parse until we either reach EOB or\r
++ ;; get the whole value\r
++ (save-excursion\r
++ (let ((pstate\r
++ (with-syntax-table notmuch-json-syntax-table\r
++ (parse-partial-sexp\r
++ (notmuch-json-partial-pos jp) (point-max) 0 nil\r
++ (notmuch-json-partial-state jp)))))\r
++ ;; A complete value is available if we've reached\r
++ ;; depth 0 or less and encountered a complete\r
++ ;; subexpression.\r
++ (if (and (<= (first pstate) 0) (third pstate))\r
++ t\r
++ ;; Not complete. Update the partial parser state\r
++ (setf (notmuch-json-partial-pos jp) (point-marker)\r
++ (notmuch-json-partial-state jp) pstate)\r
++ nil))))))\r
++\r
++ (if (not complete)\r
++ 'retry\r
++ ;; We have a value. Reset the partial parse state and expect\r
++ ;; a comma or terminator after the value.\r
++ (setf (notmuch-json-next jp) 'expect-comma\r
++ (notmuch-json-allow-term jp) t\r
++ (notmuch-json-partial-pos jp) nil\r
++ (notmuch-json-partial-state jp) nil)\r
++ ;; Parse the value\r
++ (let ((json-object-type 'plist)\r
++ (json-array-type 'list)\r
++ (json-false nil))\r
++ (json-read)))))))\r
++\r
++(defun notmuch-json-eof (jp)\r
++ "Signal a json-error if there is more input in JP's buffer.\r
++\r
++Moves point to the beginning of any trailing garbage or to the\r
++end of the buffer if there is no trailing garbage."\r
++\r
++ (with-current-buffer (notmuch-json-buffer jp)\r
++ (skip-chars-forward " \t\r\n")\r
++ (unless (eobp)\r
++ (signal 'json-error (list "Trailing garbage following JSON data")))))\r
++\r
+ (provide 'notmuch-lib)\r
+ \r
+ ;; Local Variables:\r
+-- \r
+1.7.10\r
+\r
projects / notmuch-archives.git / commitdiff