GUAC-847: Implement recursive descent parser for guacd config files.

src/guacd/Makefile.am

@@ -27,8 +27,19 @@ AM_CFLAGS = -Werror -Wall -pedantic @LIBGUAC_INCLUDE@ @COMMON_INCLUDE@
 sbin_PROGRAMS = guacd
 man_MANS = man/guacd.8
 
-noinst_HEADERS = client.h client-map.h log.h
+noinst_HEADERS = \
-guacd_SOURCES  = daemon.c client.c client-map.c log.c
+    client.h     \
+    client-map.h \
+    conf-file.h  \
+    log.h
+
+guacd_SOURCES =  \
+    daemon.c     \
+	client.c     \
+	client-map.c \
+	conf-file.c  \
+	log.c
+
 guacd_LDADD   = @LIBGUAC_LTLIB@ @COMMON_LTLIB@
 guacd_LDFLAGS = @PTHREAD_LIBS@ @SSL_LIBS@
 

src/guacd/conf-file.c

@@ -0,0 +1,513 @@
+/*
+ * Copyright (C) 2014 Glyptodon LLC
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "config.h"
+
+#include "conf-file.h"
+
+#include <ctype.h>
+#include <string.h>
+
+/*
+ * Simple recursive descent parser for an INI-like conf file grammar.  The
+ * grammar is, roughly:
+ *
+ * <line>            ::= <opt-whitespace> <declaration> <line-end>
+ * <line-end>        ::= <opt-whitespace> <opt-comment> <EOL>
+ * <declaration>     ::= <section-name> | <parameter-value> | ""
+ * <section-name>    ::= "[" <name> "]"
+ * <parameter-value> ::= <name> <opt-whitespace> "=" <opt-whitespace> <value>
+ *
+ * Where:
+ *  <opt-whitespace> is any number of tabs or spaces.
+ *  <opt-comment> is a # character followed by any length of text without an EOL.
+ *  <name> is an alpha-numeric string consisting of: [A-Za-z0-9_-].
+ *  <value> is any length of text without an EOL or # character, or a double-quoted string (backslash escapes legal).
+ *  <EOL> is a carriage return or line feed character.
+ */
+
+/**
+ * The current section. Note that this means the parser is NOT threadsafe.
+ */
+char __guacd_current_section[GUACD_CONF_MAX_NAME_LENGTH + 1] = "";
+
+char* guacd_conf_parse_error = NULL;
+
+char* guacd_conf_parse_error_location = NULL;
+
+/**
+ * Reads through all whitespace at the beginning of the buffer, returning the
+ * number of characters read. This is <opt-whitespace> in the grammar above. As
+ * the whitespace is zero or more whitespace characters, this function cannot
+ * fail, but it may read zero chars overall.
+ */
+static int guacd_parse_whitespace(char* buffer, int length) {
+
+    int chars_read = 0;
+
+    /* Read through all whitespace */
+    while (chars_read < length) {
+
+        /* Read character */
+        char c = *buffer;
+
+        /* Stop at non-whitespace */
+        if (c != ' ' && c != '\t')
+            break;
+
+        chars_read++;
+        buffer++;
+
+    }
+
+    return chars_read;
+
+}
+
+/**
+ * Parses the name of a parameter, section, etc. A section/parameter name can
+ * consist only of alphanumeric characters and underscores. The resulting name
+ * will be stored in the name string, which must have at least 256 bytes
+ * available.
+ */
+static int guacd_parse_name(char* buffer, int length, char* name) {
+
+    char* name_start = buffer;
+    int chars_read = 0;
+
+    /* Read through all valid name chars */
+    while (chars_read < length) {
+
+        /* Read character */
+        char c = *buffer;
+
+        /* Stop at non-name characters */
+        if (!isalnum(c) && c != '_')
+            break;
+
+        chars_read++;
+        buffer++;
+
+        /* Ensure name does not exceed maximum length */
+        if (chars_read > GUACD_CONF_MAX_NAME_LENGTH) {
+            guacd_conf_parse_error = "Names can be no more than 255 characters long";
+            guacd_conf_parse_error_location = buffer;
+            return -1;
+        }
+
+    }
+
+    /* Names must contain at least one character */
+    if (chars_read == 0)
+        return 0;
+
+    /* Copy name from buffer */
+    memcpy(name, name_start, chars_read);
+    name[chars_read] = '\0';
+
+    return chars_read;
+
+}
+
+/**
+ * Parses the value of a parameter. A value can consist of any character except
+ * '#', whitespace, or EOL. The resulting value will be stored in the value
+ * string, which must have at least 256 bytes available.
+ */ 
+static int guacd_parse_value(char* buffer, int length, char* value) {
+
+    char* value_start = buffer;
+    int chars_read = 0;
+
+    /* Read through all valid value chars */
+    while (chars_read < length) {
+
+        /* Read character */
+        char c = *buffer;
+
+        /* Stop at invalid character */
+        if (c == '#' || c == '"' || c == '\r' || c == '\n' || c == ' ' || c == '\t')
+            break;
+
+        chars_read++;
+        buffer++;
+
+        /* Ensure value does not exceed maximum length */
+        if (chars_read > GUACD_CONF_MAX_VALUE_LENGTH) {
+            guacd_conf_parse_error = "Values can be no more than 8191 characters long";
+            guacd_conf_parse_error_location = buffer;
+            return -1;
+        }
+
+    }
+
+    /* Values must contain at least one character */
+    if (chars_read == 0) {
+        guacd_conf_parse_error = "Unquoted values must contain at least one character";
+        guacd_conf_parse_error_location = buffer;
+        return -1;
+    }
+
+    /* Copy value from buffer */
+    memcpy(value, value_start, chars_read);
+    value[chars_read] = '\0';
+
+    return chars_read;
+
+}
+
+/**
+ * Parses the quoted value of a parameter. Quoted values may contain any
+ * character except double quotes or backslashes, which must be
+ * backslash-escaped.
+ */ 
+static int guacd_parse_quoted_value(char* buffer, int length, char* value) {
+
+    int escaped = 0;
+
+    /* Assert first character is '"' */
+    if (length == 0 || *buffer != '"')
+        return 0;
+
+    int chars_read = 1;
+    buffer++;
+    length--;
+
+    /* Read until end of quoted value */
+    while (chars_read < length) {
+
+        /* Read character */
+        char c = *buffer;
+
+        /* Handle special characters if not escaped */
+        if (!escaped) {
+
+            /* Stop at quote or invalid character */
+            if (c == '"' || c == '\r' || c == '\n')
+                break;
+
+            /* Backslash escaping */
+            else if (c == '\\')
+                escaped = 1;
+
+            else
+                *(value++) = c;
+
+        }
+
+        /* Reset escape flag */
+        else {
+            escaped = 0;
+            *(value++) = c;
+        }
+
+        chars_read++;
+        buffer++;
+
+        /* Ensure value does not exceed maximum length */
+        if (chars_read > GUACD_CONF_MAX_VALUE_LENGTH) {
+            guacd_conf_parse_error = "Values can be no more than 8191 characters long";
+            guacd_conf_parse_error_location = buffer;
+            return -1;
+        }
+
+    }
+
+    /* Assert value ends with '"' */
+    if (length == 0 || *buffer != '"') {
+        guacd_conf_parse_error = "'\"' expected";
+        guacd_conf_parse_error_location = buffer;
+        return -1;
+    }
+
+    chars_read++;
+
+    /* Terminate read value */
+    *value = '\0';
+
+    return chars_read;
+
+}
+
+/**
+ * Reads a parameter/value pair, separated by an '=' character. If the
+ * parameter/value pair is invalid for any reason, a negative value is
+ * returned.
+ */
+static int guacd_parse_parameter(guacd_param_callback* callback, char* buffer, int length) {
+
+    char param_name[GUACD_CONF_MAX_NAME_LENGTH + 1];
+    char param_value[GUACD_CONF_MAX_VALUE_LENGTH + 1];
+
+    int retval;
+    int chars_read = 0;
+
+    retval = guacd_parse_name(buffer, length, param_name);
+    if (retval < 0)
+        return -1;
+
+    /* If no name found, no parameter/value pair */
+    if (retval == 0)
+        return 0;
+
+    /* Validate presence of section header */
+    if (__guacd_current_section[0] == '\0') {
+        guacd_conf_parse_error = "Parameters must have a corresponding section";
+        guacd_conf_parse_error_location = buffer;
+        return -1;
+    }
+
+    chars_read += retval;
+    buffer += retval;
+    length -= retval;
+
+    /* Optional whitespace before '=' */
+    retval = guacd_parse_whitespace(buffer, length);
+    chars_read += retval;
+    buffer += retval;
+    length -= retval;
+
+    /* Required '=' */
+    if (length == 0 || *buffer != '=') {
+        guacd_conf_parse_error = "'=' expected";
+        guacd_conf_parse_error_location = buffer;
+        return -1;
+    }
+
+    chars_read++;
+    buffer++;
+    length--;
+
+    /* Optional whitespace before value */
+    retval = guacd_parse_whitespace(buffer, length);
+    chars_read += retval;
+    buffer += retval;
+    length -= retval;
+
+    /* Quoted parameter value */
+    retval = guacd_parse_quoted_value(buffer, length, param_value);
+    if (retval < 0)
+        return -1;
+
+    /* Non-quoted parameter value (required if no quoted value given) */
+    if (retval == 0) retval = guacd_parse_value(buffer, length, param_value);
+    if (retval < 0)
+        return -1;
+    
+    chars_read += retval;
+
+    /* Call callback, handling error code */
+    if (callback(__guacd_current_section, param_name, param_value))
+        return -1;
+
+    return chars_read;
+
+}
+
+/**
+ * Reads a section name from the beginning of the given buffer. This section
+ * name must conform to the grammar definition. If the section name does not
+ * match, a negative value is returned.
+ */
+static int guacd_parse_section(char* buffer, int length) {
+
+    int retval;
+
+    /* Assert first character is '[' */
+    if (length == 0 || *buffer != '[')
+        return 0;
+
+    int chars_read = 1;
+    buffer++;
+    length--;
+
+    retval = guacd_parse_name(buffer, length, __guacd_current_section);
+    if (retval < 0)
+        return -1;
+
+    /* If no name found, invalid section */
+    if (retval == 0) {
+        guacd_conf_parse_error = "Section names must contain at least one character";
+        guacd_conf_parse_error_location = buffer;
+        return -1;
+    }
+
+    chars_read += retval;
+    buffer += retval;
+    length -= retval;
+
+    /* Name must end with ']' */
+    if (length == 0 || *buffer != ']') {
+        guacd_conf_parse_error = "']' expected";
+        guacd_conf_parse_error_location = buffer;
+        return -1;
+    }
+
+    chars_read++;
+    
+    return chars_read;
+
+}
+
+/**
+ * Parses a declaration, which may be either a section name or a
+ * parameter/value pair. The empty string is acceptable, as well, as a
+ * "null declaration".
+ */
+static int guacd_parse_declaration(guacd_param_callback* callback, char* buffer, int length) {
+
+    int retval;
+
+    /* Look for section name */
+    retval = guacd_parse_section(buffer, length);
+    if (retval != 0)
+        return retval;
+
+    /* Lacking a section name, read parameter/value pair */
+    retval = guacd_parse_parameter(callback, buffer, length);
+    if (retval != 0)
+        return retval;
+
+    /* Null declaration (default) */
+    return 0;
+
+}
+
+/**
+ * Parses a comment, which must start with a '#' character, and terminate with
+ * an end-of-line character. If no EOL is found, or the first character is not
+ * a '#', a negative value is returned. Otherwise, the number of characters
+ * parsed is returned. If no comment is present, zero is returned.
+ */
+static int guacd_parse_comment(char* buffer, int length) {
+
+    /* Need at least one character */
+    if (length == 0)
+        return 0;
+
+    /* Assert first character is '#' */
+    if (*(buffer++) != '#')
+        return 0;
+
+    int chars_read = 1;
+
+    /* Advance to first non-space character */
+    while (chars_read < length) {
+
+        /* Read character */
+        char c = *buffer;
+
+        /* End of comment found at end of line */
+        if (c == '\n' || c == '\r')
+            return chars_read;
+
+        chars_read++;
+        buffer++;
+
+    }
+
+    /* No end of line in comment */
+    guacd_conf_parse_error = "expected end-of-line";
+    guacd_conf_parse_error_location = buffer;
+    return -1;
+
+}
+
+/**
+ * Parses the end of a line, which may contain a comment. If a parse error
+ * occurs, a negative value is returned. Otherwise, the number of characters
+ * parsed is returned.
+ */
+static int guacd_parse_line_end(char* buffer, int length) {
+
+    int chars_read = 0;
+    int retval;
+  
+    /* Initial optional whitespace */ 
+    retval = guacd_parse_whitespace(buffer, length);
+    chars_read += retval;
+    buffer += retval;
+    length -= retval;
+
+    /* Optional comment */ 
+    retval = guacd_parse_comment(buffer, length);
+    if (retval < 0)
+        return -1;
+
+    chars_read += retval;
+    buffer += retval;
+    length -= retval;
+
+    /* Assert EOL */
+    if (length == 0 || (*buffer != '\r' && *buffer != '\n')) {
+        guacd_conf_parse_error = "expected end-of-line";
+        guacd_conf_parse_error_location = buffer;
+        return -1;
+    }
+
+    chars_read++;
+
+    /* Line is valid */
+    return chars_read;
+
+}
+
+/**
+ * Parses an entire line - declaration, comment, and all. If a parse error
+ * occurs, a negative value is returned. Otherwise, the number of characters
+ * parsed is returned.
+ */
+static int guacd_parse_line(guacd_param_callback* callback, char* buffer, int length) {
+
+    int chars_read = 0;
+    int retval;
+  
+    /* Initial optional whitespace */ 
+    retval = guacd_parse_whitespace(buffer, length);
+    chars_read += retval;
+    buffer += retval;
+    length -= retval;
+
+    /* Declaration (which may be the empty string) */
+    retval = guacd_parse_declaration(callback, buffer, length);
+    if (retval < 0)
+        return retval;
+
+    chars_read += retval;
+    buffer += retval;
+    length -= retval;
+
+    /* End of line */
+    retval = guacd_parse_line_end(buffer, length);
+    if (retval < 0)
+        return retval;
+
+    chars_read += retval;
+
+    return chars_read;
+
+}
+
+int guacd_parse_conf(guacd_param_callback* callback, char* buffer, int length) {
+    return guacd_parse_line(callback, buffer, length);
+}
+

src/guacd/conf-file.h

@@ -0,0 +1,64 @@
+/*
+ * Copyright (C) 2014 Glyptodon LLC
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#ifndef _GUACD_CONF_FILE_H
+#define _GUACD_CONF_FILE_H
+
+/**
+ * The maximum length of a name, in characters.
+ */
+#define GUACD_CONF_MAX_NAME_LENGTH 255
+
+/**
+ * The maximum length of a value, in characters.
+ */
+#define GUACD_CONF_MAX_VALUE_LENGTH 8191 
+
+/**
+ * A callback function which is provided to guacd_parse_conf() and is called
+ * for each parameter/value pair set. The current section is always given. This
+ * function will not be called for parameters outside of sections, which are
+ * illegal.
+ */
+typedef int guacd_param_callback(const char* section, const char* param, const char* value);
+
+/**
+ * Parses an arbitrary buffer of configuration file data, calling the given
+ * callback for each valid parameter/value pair. Upon success, the number of
+ * characters parsed is returned. On failure, a negative value is returned, and
+ * guacd_conf_parse_error and guacd_conf_parse_error_location are set.
+ */
+int guacd_parse_conf(guacd_param_callback* callback, char* buffer, int length);
+
+/**
+ * Human-readable description of the current error, if any.
+ */
+extern char* guacd_conf_parse_error;
+
+/**
+ * The location of the most recent parse error. This will be a pointer to the
+ * location of the error within the buffer passed to guacd_parse_conf().
+ */
+extern char* guacd_conf_parse_error_location;
+
+#endif
+