fix: handle Gmail raw response streams correctly

FlowCrypt/src/main/java/com/flowcrypt/email/api/email/gmail/api/GMailRawAttachmentFilterInputStream.kt

@@ -1,37 +1,18 @@
 /*
  * © 2016-present FlowCrypt a.s. Limitations apply. Contact human@flowcrypt.com
- * Contributors: DenBond7
+ * Contributors: denbond7
  */
 
 package com.flowcrypt.email.api.email.gmail.api
 
-import java.io.FilterInputStream
 import java.io.InputStream
 
 /**
  * @author Denys Bondarenko
  */
 class GMailRawAttachmentFilterInputStream(inputStream: InputStream) :
-  FilterInputStream(inputStream) {
-  init {
-    skip(9)
-  }
-
-  /**
-   * Via this method we trim the end of the stream
-   */
-  override fun read(b: ByteArray, off: Int, len: Int): Int {
-    val tempBuffer = b.copyOf()
-    val i = super.read(tempBuffer, off, len)
-    //find index of the last '"' char
-    val indexEndStart = tempBuffer.indexOf(34)
-
-    return if (indexEndStart != -1) {
-      tempBuffer.copyInto(b, endIndex = indexEndStart)
-      indexEndStart
-    } else {
-      tempBuffer.copyInto(b)
-      i
-    }
+  GMailRawResponseFilterInputStream(inputStream, JSON_PREFIX_LENGTH) {
+  private companion object {
+    const val JSON_PREFIX_LENGTH = 9L
   }
 }

FlowCrypt/src/main/java/com/flowcrypt/email/api/email/gmail/api/GMailRawMIMEMessageFilterInputStream.kt

@@ -1,38 +1,18 @@
 /*
  * © 2016-present FlowCrypt a.s. Limitations apply. Contact human@flowcrypt.com
- * Contributors: DenBond7
+ * Contributors: denbond7
  */
 
 package com.flowcrypt.email.api.email.gmail.api
 
-import java.io.FilterInputStream
 import java.io.InputStream
 
 /**
  * @author Denys Bondarenko
  */
 class GMailRawMIMEMessageFilterInputStream(inputStream: InputStream) :
-  FilterInputStream(inputStream) {
-  init {
-    // we should skip first 12 bytes to begin to read raw MIME message as a stream
-    skip(12)
-  }
-
-  /**
-   * Via this method we trim the end of the stream
-   */
-  override fun read(b: ByteArray, off: Int, len: Int): Int {
-    val tempBuffer = b.copyOf()
-    val i = super.read(tempBuffer, off, len)
-    //find index of the last '"' char
-    val indexEndStart = tempBuffer.indexOf(34)
-
-    return if (indexEndStart != -1) {
-      tempBuffer.copyInto(b, endIndex = indexEndStart)
-      indexEndStart
-    } else {
-      tempBuffer.copyInto(b)
-      i
-    }
+  GMailRawResponseFilterInputStream(inputStream, JSON_PREFIX_LENGTH) {
+  private companion object {
+    const val JSON_PREFIX_LENGTH = 12L
   }
 }

FlowCrypt/src/main/java/com/flowcrypt/email/api/email/gmail/api/GMailRawResponseFilterInputStream.kt

@@ -0,0 +1,86 @@
+/*
+ * © 2016-present FlowCrypt a.s. Limitations apply. Contact human@flowcrypt.com
+ * Contributors: denbond7
+ */
+
+package com.flowcrypt.email.api.email.gmail.api
+
+import java.io.EOFException
+import java.io.FilterInputStream
+import java.io.InputStream
+
+/**
+ * Exposes the Base64URL value from a Gmail API JSON response as an input stream.
+ *
+ * The opening JSON bytes are removed by [prefixLength]. The first quote after the prefix terminates
+ * the value because the Base64URL alphabet cannot contain quotes.
+ */
+open class GMailRawResponseFilterInputStream(
+  inputStream: InputStream,
+  prefixLength: Long
+) : FilterInputStream(inputStream) {
+  private var endReached = false
+
+  init {
+    skipFully(prefixLength)
+  }
+
+  override fun read(): Int {
+    if (endReached) return -1
+
+    return when (val value = super.read()) {
+      -1 -> -1
+      JSON_STRING_DELIMITER -> {
+        endReached = true
+        -1
+      }
+
+      else -> value
+    }
+  }
+
+  override fun read(b: ByteArray, off: Int, len: Int): Int {
+    checkBounds(b, off, len)
+    if (len == 0) return 0
+    if (endReached) return -1
+
+    val readCount = super.read(b, off, len)
+    if (readCount <= 0) return readCount
+
+    for (index in off until off + readCount) {
+      if (b[index].toInt() == JSON_STRING_DELIMITER) {
+        endReached = true
+        val valueLength = index - off
+        return if (valueLength == 0) -1 else valueLength
+      }
+    }
+
+    return readCount
+  }
+
+  private fun skipFully(byteCount: Long) {
+    var remaining = byteCount
+    while (remaining > 0) {
+      val skipped = super.skip(remaining)
+      if (skipped > 0) {
+        remaining -= skipped
+      } else if (super.read() == -1) {
+        throw EOFException("Unexpected end of Gmail API response while skipping JSON prefix")
+      } else {
+        remaining--
+      }
+    }
+  }
+
+  private fun checkBounds(buffer: ByteArray, offset: Int, length: Int) {
+    if (offset < 0 || length < 0 || length > buffer.size - offset) {
+      throw IndexOutOfBoundsException(
+        "offset=$offset, length=$length, bufferSize=${buffer.size}"
+      )
+    }
+  }
+
+  private companion object {
+    const val JSON_STRING_DELIMITER = '"'.code
+  }
+}

FlowCrypt/src/test/java/com/flowcrypt/email/api/email/gmail/api/GMailRawResponseFilterInputStreamTest.kt

@@ -0,0 +1,97 @@
+/*
+ * © 2016-present FlowCrypt a.s. Limitations apply. Contact human@flowcrypt.com
+ * Contributors: denbond7
+ */
+
+package com.flowcrypt.email.api.email.gmail.api
+
+import org.junit.Assert.assertArrayEquals
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertThrows
+import org.junit.Test
+import java.io.ByteArrayInputStream
+import java.io.EOFException
+
+class GMailRawResponseFilterInputStreamTest {
+  @Test
+  fun testAttachmentResponseReadInSmallChunks() {
+    val stream = GMailRawAttachmentFilterInputStream(
+      """{"data":"YWJjZA=="}""".byteInputStream()
+    )
+
+    assertEquals("YWJjZA==", stream.readBytesWithChunkSize(2).decodeToString())
+    assertEquals(-1, stream.read())
+  }
+
+  @Test
+  fun testMimeResponseReadOneByteAtATime() {
+    val stream = GMailRawMIMEMessageFilterInputStream(
+      "{\n  \"raw\": \"YWJjZA==\"\n}\n".byteInputStream()
+    )
+
+    val result = buildList {
+      while (true) {
+        val value = stream.read()
+        if (value == -1) break
+        add(value.toByte())
+      }
+    }.toByteArray()
+
+    assertEquals("YWJjZA==", result.decodeToString())
+    assertEquals(-1, stream.read())
+  }
+
+  @Test
+  fun testBulkReadHonorsOffsetAndIgnoresExistingBufferContent() {
+    val stream = GMailRawAttachmentFilterInputStream(
+      """{"data":"YWJj"}""".byteInputStream()
+    )
+    val buffer = ByteArray(10) { '"'.code.toByte() }
+
+    val count = stream.read(buffer, 3, 4)
+
+    assertEquals(4, count)
+    assertArrayEquals("YWJj".toByteArray(), buffer.copyOfRange(3, 7))
+    assertEquals(-1, stream.read(buffer, 3, 4))
+  }
+
+  @Test
+  fun testPrefixIsFullyConsumedWhenDelegateSkipMakesPartialProgress() {
+    val response = """{"data":"YWJj"}""".toByteArray()
+    val delegate = object : ByteArrayInputStream(response) {
+      override fun skip(n: Long): Long = super.skip(n.coerceAtMost(1))
+    }
+
+    val stream = GMailRawAttachmentFilterInputStream(delegate)
+
+    assertEquals("YWJj", stream.readBytes().decodeToString())
+  }
+
+  @Test
+  fun testTruncatedPrefixThrows() {
+    assertThrows(EOFException::class.java) {
+      GMailRawAttachmentFilterInputStream("{}".byteInputStream())
+    }
+  }
+
+  @Test
+  fun testEmptyValueReturnsEndOfStream() {
+    val stream = GMailRawAttachmentFilterInputStream("""{"data":""}""".byteInputStream())
+
+    assertEquals(-1, stream.read(ByteArray(8), 0, 8))
+    assertEquals(-1, stream.read())
+  }
+
+  private fun GMailRawResponseFilterInputStream.readBytesWithChunkSize(
+    chunkSize: Int
+  ): ByteArray {
+    val result = mutableListOf<Byte>()
+    val buffer = ByteArray(chunkSize)
+    while (true) {
+      val count = read(buffer, 0, buffer.size)
+      if (count == -1) break
+      result.addAll(buffer.copyOf(count).toList())
+    }
+    return result.toByteArray()
+  }
+}