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diff --git a/lib/nghttp3_qpack_huffman.h b/lib/nghttp3_qpack_huffman.h
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+++ b/lib/nghttp3_qpack_huffman.h
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+/*
+ * nghttp3
+ *
+ * Copyright (c) 2019 nghttp3 contributors
+ * Copyright (c) 2013 nghttp2 contributors
+ *
+ * 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 NGHTTP3_QPACK_HUFFMAN_H
+#define NGHTTP3_QPACK_HUFFMAN_H
+
+#ifdef HAVE_CONFIG_H
+#  include <config.h>
+#endif /* HAVE_CONFIG_H */
+
+#include <nghttp3/nghttp3.h>
+
+typedef struct nghttp3_qpack_huffman_sym {
+  /* The number of bits in this code */
+  uint32_t nbits;
+  /* Huffman code aligned to LSB */
+  uint32_t code;
+} nghttp3_qpack_huffman_sym;
+
+extern const nghttp3_qpack_huffman_sym huffman_sym_table[];
+
+size_t nghttp3_qpack_huffman_encode_count(const uint8_t *src, size_t len);
+
+uint8_t *nghttp3_qpack_huffman_encode(uint8_t *dest, const uint8_t *src,
+                                      size_t srclen);
+
+typedef enum nghttp3_qpack_huffman_decode_flag {
+  /* FSA accepts this state as the end of huffman encoding
+     sequence. */
+  NGHTTP3_QPACK_HUFFMAN_ACCEPTED = 1 << 14,
+  /* This state emits symbol */
+  NGHTTP3_QPACK_HUFFMAN_SYM = 1 << 15,
+} nghttp3_qpack_huffman_decode_flag;
+
+typedef struct nghttp3_qpack_huffman_decode_node {
+  /* fstate is the current huffman decoding state, which is actually
+     the node ID of internal huffman tree with
+     nghttp3_qpack_huffman_decode_flag OR-ed.  We have 257 leaf nodes,
+     but they are identical to root node other than emitting a symbol,
+     so we have 256 internal nodes [1..256], inclusive.  The node ID
+     256 is a special node and it is a terminal state that means
+     decoding failed. */
+  uint16_t fstate;
+  /* symbol if NGHTTP3_QPACK_HUFFMAN_SYM flag set */
+  uint8_t sym;
+} nghttp3_qpack_huffman_decode_node;
+
+typedef struct nghttp3_qpack_huffman_decode_context {
+  /* fstate is the current huffman decoding state. */
+  uint16_t fstate;
+} nghttp3_qpack_huffman_decode_context;
+
+extern const nghttp3_qpack_huffman_decode_node qpack_huffman_decode_table[][16];
+
+void nghttp3_qpack_huffman_decode_context_init(
+    nghttp3_qpack_huffman_decode_context *ctx);
+
+/*
+ * nghttp3_qpack_huffman_decode decodes huffman encoded byte string
+ * stored in |src| of length |srclen|.  |ctx| is a decoding context.
+ * |ctx| remembers the decoding state, and caller can call this
+ * function multiple times to feed each chunk of huffman encoded
+ * substring.  |fin| must be nonzero if |src| contains the last chunk
+ * of huffman string.  The decoded string is written to the buffer
+ * pointed by |dest|.  This function assumes that the buffer pointed
+ * by |dest| contains enough memory to store decoded byte string.
+ *
+ * This function returns the number of bytes written to |dest|, or one
+ * of the following negative error codes:
+ *
+ * NGHTTP3_ERR_QPACK_FATAL
+ *     Could not decode huffman string.
+ */
+nghttp3_ssize
+nghttp3_qpack_huffman_decode(nghttp3_qpack_huffman_decode_context *ctx,
+                             uint8_t *dest, const uint8_t *src, size_t srclen,
+                             int fin);
+
+/*
+ * nghttp3_qpack_huffman_decode_failure_state returns nonzero if |ctx|
+ * indicates that huffman decoding context is in failure state.
+ */
+int nghttp3_qpack_huffman_decode_failure_state(
+    nghttp3_qpack_huffman_decode_context *ctx);
+
+#endif /* NGHTTP3_QPACK_HUFFMAN_H */