ccdetect: extract CDP parser to a separate module

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/474>

3 files changed, 157 insertions, 134 deletions

diff --git a/video/closedcaption/src/ccdetect/imp.rs b/video/closedcaption/src/ccdetect/imp.rs
index deaa430b2..c19b537c1 100644
--- a/video/closedcaption/src/ccdetect/imp.rs
+++ b/video/closedcaption/src/ccdetect/imp.rs
@@ -22,11 +22,9 @@ use gst::subclass::prelude::*;
 use gst::{gst_trace, gst_warning};
 use gst_base::subclass::prelude::*;
 
-use byteorder::{BigEndian, ByteOrder};
-
+use crate::ccutils::{extract_cdp, ParseError, ParseErrorCode};
 use once_cell::sync::Lazy;
 
-use std::fmt;
 use std::sync::Mutex;
 use std::u64;
 
@@ -83,29 +81,6 @@ struct CCPacketContents {
     cc708: bool,
 }
 
-#[allow(clippy::enum_variant_names)]
-#[derive(Debug, Clone, Copy)]
-enum ParseErrorCode {
-    WrongLength,
-    WrongMagicSequence,
-    WrongLayout,
-}
-
-#[derive(Debug, Clone)]
-struct ParseError {
-    code: ParseErrorCode,
-    byte: usize,
-    msg: String,
-}
-
-impl fmt::Display for ParseError {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "{:?} at byte {}: {}", self.code, self.byte, self.msg)
-    }
-}
-
-impl std::error::Error for ParseError {}
-
 impl CCDetect {
     fn detect_cc_data(data: &[u8]) -> Result<CCPacketContents, ParseError> {
         if data.len() % 3 != 0 {
@@ -172,115 +147,10 @@ impl CCDetect {
         })
     }
 
-    fn detect_cdp(mut data: &[u8]) -> Result<CCPacketContents, ParseError> {
-        /* logic from ccconverter */
-        let data_len = data.len();
-
-        if data.len() < 11 {
-            return Err(ParseError {
-                code: ParseErrorCode::WrongLength,
-                byte: data_len - data.len(),
-                msg: format!(
-                    "cdp packet too short {}. expected at least {}",
-                    data.len(),
-                    11
-                ),
-            });
-        }
-
-        if 0x9669 != BigEndian::read_u16(&data[..2]) {
-            return Err(ParseError {
-                code: ParseErrorCode::WrongMagicSequence,
-                byte: data_len - data.len(),
-                msg: String::from("cdp packet does not have initial magic bytes of 0x9669"),
-            });
-        }
-        data = &data[2..];
-
-        if (data[0] as usize) != data_len {
-            return Err(ParseError {
-                code: ParseErrorCode::WrongLength,
-                byte: data_len - data.len(),
-                msg: format!(
-                    "advertised cdp packet length {} does not match length of data {}",
-                    data[0], data_len
-                ),
-            });
-        }
-        data = &data[1..];
-
-        /* skip framerate value */
-        data = &data[1..];
-
-        let flags = data[0];
-        data = &data[1..];
-
-        if flags & 0x40 == 0 {
-            /* no cc_data */
-            return Ok(CCPacketContents {
-                cc608: false,
-                cc708: false,
-            });
-        }
-
-        /* skip sequence counter */
-        data = &data[2..];
-
-        /* timecode present? */
-        if flags & 0x80 == 0x80 {
-            if data.len() < 5 {
-                return Err(ParseError {
-                    code: ParseErrorCode::WrongLength,
-                    byte: data_len - data.len(),
-                    msg: String::from("cdp packet signals a timecode but is not large enough to contain a timecode")
-                });
-            }
-            data = &data[5..];
-        }
-
-        /* cc_data */
-        if data.len() < 2 {
-            return Err(ParseError {
-                code: ParseErrorCode::WrongLength,
-                byte: data_len - data.len(),
-                msg: String::from(
-                    "cdp packet signals cc_data but is not large enough to contain cc_data",
-                ),
-            });
-        }
-
-        if data[0] != 0x72 {
-            return Err(ParseError {
-                code: ParseErrorCode::WrongMagicSequence,
-                byte: data_len - data.len(),
-                msg: String::from("ccp is missing start code 0x72"),
-            });
-        }
-        data = &data[1..];
-
-        let cc_count = data[0];
-        data = &data[1..];
-        if cc_count & 0xe0 != 0xe0 {
-            return Err(ParseError {
-                code: ParseErrorCode::WrongMagicSequence,
-                byte: data_len - data.len(),
-                msg: format!("reserved bits are not 0xe0, found {:02x}", cc_count & 0xe0),
-            });
-        }
-        let cc_count = cc_count & 0x1f;
-        let len = 3 * cc_count as usize;
-
-        if len > data.len() {
-            return Err(ParseError {
-                code: ParseErrorCode::WrongLength,
-                byte: data_len - data.len(),
-                msg: String::from("cc_data length extends past the end of the cdp packet"),
-            });
-        }
-
-        /* TODO: validate checksum */
+    fn detect_cdp(data: &[u8]) -> Result<CCPacketContents, ParseError> {
+        let data = extract_cdp(data)?;
 
-        Self::detect_cc_data(&data[..len])
+        Self::detect_cc_data(data)
     }
 
     fn detect(format: CCFormat, data: &[u8]) -> Result<CCPacketContents, ParseError> {
diff --git a/video/closedcaption/src/ccutils.rs b/video/closedcaption/src/ccutils.rs
new file mode 100644
index 000000000..8d7fdadfd
--- /dev/null
+++ b/video/closedcaption/src/ccutils.rs
@@ -0,0 +1,152 @@
+// Copyright (C) 2020 Matthew Waters <matthew@centricular.com>
+//
+// This library is free software; you can redistribute it and/or
+// modify it under the terms of the GNU Library General Public
+// License as published by the Free Software Foundation; either
+// version 2 of the License, or (at your option) any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// Library General Public License for more details.
+//
+// You should have received a copy of the GNU Library General Public
+// License along with this library; if not, write to the
+// Free Software Foundation, Inc., 51 Franklin Street, Suite 500,
+// Boston, MA 02110-1335, USA.
+
+use byteorder::{BigEndian, ByteOrder};
+use std::fmt;
+
+#[allow(clippy::enum_variant_names)]
+#[derive(Debug, Clone, Copy)]
+pub enum ParseErrorCode {
+    WrongLength,
+    WrongMagicSequence,
+    WrongLayout,
+}
+
+#[derive(Debug, Clone)]
+pub struct ParseError {
+    pub code: ParseErrorCode,
+    pub byte: usize,
+    pub msg: String,
+}
+
+pub fn extract_cdp(mut data: &[u8]) -> Result<&[u8], ParseError> {
+    /* logic from ccconverter */
+    let data_len = data.len();
+
+    if data.len() < 11 {
+        return Err(ParseError {
+            code: ParseErrorCode::WrongLength,
+            byte: data_len - data.len(),
+            msg: format!(
+                "cdp packet too short {}. expected at least {}",
+                data.len(),
+                11
+            ),
+        });
+    }
+
+    if 0x9669 != BigEndian::read_u16(&data[..2]) {
+        return Err(ParseError {
+            code: ParseErrorCode::WrongMagicSequence,
+            byte: data_len - data.len(),
+            msg: String::from("cdp packet does not have initial magic bytes of 0x9669"),
+        });
+    }
+    data = &data[2..];
+
+    if (data[0] as usize) != data_len {
+        return Err(ParseError {
+            code: ParseErrorCode::WrongLength,
+            byte: data_len - data.len(),
+            msg: format!(
+                "advertised cdp packet length {} does not match length of data {}",
+                data[0], data_len
+            ),
+        });
+    }
+    data = &data[1..];
+
+    /* skip framerate value */
+    data = &data[1..];
+
+    let flags = data[0];
+    data = &data[1..];
+
+    if flags & 0x40 == 0 {
+        /* no cc_data */
+        return Ok(&[]);
+    }
+
+    /* skip sequence counter */
+    data = &data[2..];
+
+    /* timecode present? */
+    if flags & 0x80 == 0x80 {
+        if data.len() < 5 {
+            return Err(ParseError {
+                code: ParseErrorCode::WrongLength,
+                byte: data_len - data.len(),
+                msg: String::from(
+                    "cdp packet signals a timecode but is not large enough to contain a timecode",
+                ),
+            });
+        }
+        data = &data[5..];
+    }
+
+    /* cc_data */
+    if data.len() < 2 {
+        return Err(ParseError {
+            code: ParseErrorCode::WrongLength,
+            byte: data_len - data.len(),
+            msg: String::from(
+                "cdp packet signals cc_data but is not large enough to contain cc_data",
+            ),
+        });
+    }
+
+    if data[0] != 0x72 {
+        return Err(ParseError {
+            code: ParseErrorCode::WrongMagicSequence,
+            byte: data_len - data.len(),
+            msg: String::from("ccp is missing start code 0x72"),
+        });
+    }
+    data = &data[1..];
+
+    let cc_count = data[0];
+    data = &data[1..];
+    if cc_count & 0xe0 != 0xe0 {
+        return Err(ParseError {
+            code: ParseErrorCode::WrongMagicSequence,
+            byte: data_len - data.len(),
+            msg: format!("reserved bits are not 0xe0, found {:02x}", cc_count & 0xe0),
+        });
+    }
+    let cc_count = cc_count & 0x1f;
+    let len = 3 * cc_count as usize;
+
+    if len > data.len() {
+        return Err(ParseError {
+            code: ParseErrorCode::WrongLength,
+            byte: data_len - data.len(),
+            msg: String::from("cc_data length extends past the end of the cdp packet"),
+        });
+    }
+
+    /* TODO: validate checksum */
+
+    Ok(&data[..len])
+}
+
+impl fmt::Display for ParseError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{:?} at byte {}: {}", self.code, self.byte, self.msg)
+    }
+}
+
+impl std::error::Error for ParseError {}
diff --git a/video/closedcaption/src/lib.rs b/video/closedcaption/src/lib.rs
index 84fa5b7ac..30b8e74ed 100644
--- a/video/closedcaption/src/lib.rs
+++ b/video/closedcaption/src/lib.rs
@@ -24,6 +24,7 @@ mod ffi;
 
 mod caption_frame;
 mod ccdetect;
+mod ccutils;
 mod cea608overlay;
 mod cea608tott;
 mod line_reader;