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Count HPACK header list entries with RFC 9113 per-entry overhead #9733

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Count HPACK header list entries with RFC 9113 per-entry overhead #9733

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9 changes: 8 additions & 1 deletion okhttp/src/commonJvmAndroid/kotlin/okhttp3/internal/http2/Hpack.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -47,6 +47,11 @@ object Hpack {
private const val PREFIX_6_BITS = 0x3f
private const val PREFIX_7_BITS = 0x7f

/**
* Per-entry overhead of a header list entry, as defined by RFC 9113 section 6.5.2.
*/
private const val HEADER_ENTRY_OVERHEAD = 32

private const val SETTINGS_HEADER_TABLE_SIZE = 4_096

/**
Expand Down Expand Up @@ -411,7 +416,9 @@ object Hpack {
private fun addHeader(header: Header) {
headerList.add(header)

val headerSize = header.name.size + header.value.size
// Include the per-entry overhead of RFC 9113 section 6.5.2, so the accounting
// also grows for headers whose name and value are both empty.
val headerSize = header.name.size + header.value.size + HEADER_ENTRY_OVERHEAD
val newHeaderListSize = headerListByteCount + headerSize
headerListByteCount = newHeaderListSize
if (newHeaderListSize > HEADER_LIMIT) {
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18 changes: 18 additions & 0 deletions okhttp/src/jvmTest/kotlin/okhttp3/internal/http2/HpackTest.kt
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Expand Up @@ -36,6 +36,24 @@ class HpackTest {
private val bytesOut = Buffer()
private var hpackWriter: Hpack.Writer? = null

/**
* Each header list entry must account for the RFC 9113 section 6.5.2 per-entry overhead,
* including headers whose name and value are both empty. Otherwise a peer could flood
* zero-length literal header fields and grow the header list without ever exceeding
* [HEADER_LIMIT].
*/
@Test
fun manyEmptyHeadersExceedByteLimit() {
repeat(8193) {
bytesIn.writeByte(0x00) // Literal Header Field without Indexing, new name.
bytesIn.writeByte(0x00) // Name length 0.
bytesIn.writeByte(0x00) // Value length 0.
}
assertFailsWith<IOException> {
hpackReader!!.readHeaders()
}
}

@BeforeEach
fun reset() {
hpackReader = newReader(bytesIn)
Expand Down