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minimal_multipart_parser.c

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+//
+// minimal_multipart_parser.c
+//
+// Copyright (c) 2024 Brian Khuu https://briankhuu.com/
+// MIT licensed
+//
+// https://github.com/mofosyne/minimal-multipart-form-data-parser-c
+//
+
+#include "minimal_multipart_parser.h"
+#include <stdbool.h>
+
+static inline unsigned int buffer_count(MinimalMultipartParserCharBuffer *context) { return context->count; }
+
+static inline void buffer_reset(MinimalMultipartParserCharBuffer *context)
+{
+    context->buffer[0] = '\0';
+    context->count = 0;
+}
+
+static inline bool buffer_add(MinimalMultipartParserCharBuffer *context, const char c)
+{
+    if (context->count >= MINIMAL_MULTIPART_PARSER_FULL_BOUNDARY_BUFFER_MAX_CHAR)
+    {
+        return false;
+    }
+
+    context->buffer[context->count] = c;
+    context->buffer[context->count + 1] = '\0';
+    context->count++;
+    return true;
+}
+
+MultipartParserEvent minimal_multipart_parser_process(MinimalMultipartParserContext *context, const char c)
+{
+    MinimalMultipartParserCharBuffer *boundaryBuffer = &(context->boundary);
+    MinimalMultipartParserCharBuffer *dataBuffer = &(context->data);
+
+    if (context->data_available)
+    {
+        buffer_reset(dataBuffer);
+        context->data_available = false;
+    }
+
+    if (context->phase == MultipartParserPhase_INIT)
+    {
+        switch (c)
+        {
+            case '\r':
+                context->phase = MultipartParserPhase_Preamble_CR;
+                return MultipartParserEvent_None;
+            case '-':
+                context->phase = MultipartParserPhase_Preamble_HYPHEN;
+                return MultipartParserEvent_None;
+            default:
+                context->phase = MultipartParserPhase_Preamble_SKIP_LINE;
+                return MultipartParserEvent_None;
+        }
+    }
+
+    if (context->phase == MultipartParserPhase_Preamble_SKIP_LINE)
+    {
+        switch (c)
+        {
+            case '\r':
+                context->phase = MultipartParserPhase_Preamble_CR;
+                return MultipartParserEvent_None;
+            case '\n':
+                context->phase = MultipartParserPhase_Preamble_LF;
+                return MultipartParserEvent_None;
+            default:
+                return MultipartParserEvent_None;
+        }
+    }
+
+    if (context->phase == MultipartParserPhase_Preamble_CR)
+    {
+        switch (c)
+        {
+            case '\n':
+                context->phase = MultipartParserPhase_Preamble_LF;
+                return MultipartParserEvent_None;
+            default:
+                context->phase = MultipartParserPhase_Preamble_SKIP_LINE;
+                return MultipartParserEvent_None;
+        }
+    }
+
+    if (context->phase == MultipartParserPhase_Preamble_LF)
+    {
+        switch (c)
+        {
+            case '-':
+                context->phase = MultipartParserPhase_Preamble_HYPHEN;
+                return MultipartParserEvent_None;
+            default:
+                context->phase = MultipartParserPhase_Preamble_SKIP_LINE;
+                return MultipartParserEvent_None;
+        }
+    }
+
+    if (context->phase == MultipartParserPhase_Preamble_HYPHEN)
+    {
+        // Previously got a dash in '\r\n--', seeking another dash
+        switch (c)
+        {
+            case '-':
+                context->phase = MultipartParserPhase_GetBoundary;
+                buffer_add(boundaryBuffer, '\r');
+                buffer_add(boundaryBuffer, '\n');
+                buffer_add(boundaryBuffer, '-');
+                buffer_add(boundaryBuffer, '-');
+                return MultipartParserEvent_None;
+            default:
+                context->phase = MultipartParserPhase_Preamble_SKIP_LINE;
+                return MultipartParserEvent_None;
+        }
+    }
+
+    if (context->phase == MultipartParserPhase_GetBoundary)
+    {
+        switch (c)
+        {
+            case '\r':
+                context->phase = MultipartParserPhase_GetBoundary_Done;
+                return MultipartParserEvent_None;
+            default:
+                if ((c < ' ') || ('~' < c))
+                {
+                    context->phase = MultipartParserPhase_Preamble_SKIP_LINE;
+                    buffer_reset(dataBuffer);
+                    return MultipartParserEvent_None;
+                }
+                if (!buffer_add(boundaryBuffer, c))
+                {
+                    context->phase = MultipartParserPhase_Preamble_SKIP_LINE;
+                    buffer_reset(dataBuffer);
+                    return MultipartParserEvent_None;
+                }
+                return MultipartParserEvent_None;
+        }
+    }
+
+    if (context->phase == MultipartParserPhase_GetBoundary_Done)
+    {
+        switch (c)
+        {
+            case '\n':
+                context->phase = MultipartParserPhase_SkipFileHeader;
+                return MultipartParserEvent_FileStreamFound;
+            default:
+                context->phase = MultipartParserPhase_Preamble_SKIP_LINE;
+                buffer_reset(dataBuffer);
+                return MultipartParserEvent_None;
+        }
+    }
+
+    if (context->phase == MultipartParserPhase_SkipFileHeader)
+    {
+        const unsigned expected_index = buffer_count(dataBuffer);
+        const char expected_char = (MINIMAL_MULTIPART_PARSER_FILE_START_MARKER)[expected_index];
+        if (c != expected_char)
+        {
+            buffer_reset(dataBuffer);
+            return MultipartParserEvent_None;
+        }
+
+        buffer_add(dataBuffer, c);
+        if (buffer_count(dataBuffer) >= MINIMAL_MULTIPART_PARSER_FILE_START_MARKER_COUNT)
+        {
+            context->phase = MultipartParserPhase_GetFileBytes;
+            buffer_reset(dataBuffer);
+            return MultipartParserEvent_FileStreamStarting;
+        }
+
+        return MultipartParserEvent_None;
+    }
+
+    if (context->phase == MultipartParserPhase_GetFileBytes)
+    {
+        const unsigned char full_boundary_size = buffer_count(boundaryBuffer);
+        const char *full_boundary_string = context->boundary.buffer;
+
+        const unsigned expected_index = buffer_count(dataBuffer);
+        const char expected_char = full_boundary_string[expected_index];
+
+        buffer_add(dataBuffer, c);
+
+        if (c != expected_char)
+        {
+            context->data_available = true;
+            return MultipartParserEvent_DataBufferAvailable;
+        }
+
+        if (buffer_count(dataBuffer) >= full_boundary_size)
+        {
+            context->phase = MultipartParserPhase_EndOfFile;
+            return MultipartParserEvent_DataStreamCompleted;
+        }
+
+        return MultipartParserEvent_None;
+    }
+
+    if (context->phase == MultipartParserPhase_EndOfFile)
+    {
+        // Do nothing... We already got the file now
+        return MultipartParserEvent_DataStreamCompleted;
+    }
+
+    return MultipartParserEvent_None;
+}