From 2c96172e9dc71e4110b3c39c9beb4c6d1ed999ed Mon Sep 17 00:00:00 2001
From: Timothy Warren <twarren@nabancard.com>
Date: Tue, 1 Dec 2020 09:32:18 -0500
Subject: [PATCH] Encapsulate header parsing logic

---
 src/error.rs  |  2 +-
 src/header.rs | 44 +++++++++++++++++++++++++++++++++++++++++---
 src/lib.rs    |  2 +-
 src/main.rs   | 11 +++++------
 4 files changed, 48 insertions(+), 11 deletions(-)

diff --git a/src/error.rs b/src/error.rs
index 2c6db91..ca56d57 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -21,4 +21,4 @@ impl fmt::Display for Error {
     }
 }
 
-impl std::error::Error for Error {}
\ No newline at end of file
+impl std::error::Error for Error {}
diff --git a/src/header.rs b/src/header.rs
index d7785ea..5aef665 100644
--- a/src/header.rs
+++ b/src/header.rs
@@ -6,6 +6,29 @@ static HEADER_STRING: &[u8] = &[
     83, 81, 76, 105, 116, 101, 32, 102, 111, 114, 109, 97, 116, 32, 51, 0,
 ];
 
+/// A value stored as a Write Format Verson or
+/// Read Format Version
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord)]
+pub enum FormatVersion {
+    /// Represents the rollback journal mode
+    Legacy,
+    /// Represents the Write Ahead Log mode
+    WriteAheadLog,
+    /// Represents any mode not 1 or 2, the value
+    /// will be provided
+    Unknown(u8),
+}
+
+impl From<u8> for FormatVersion {
+    fn from(v: u8) -> Self {
+        match v {
+            1 => Self::Legacy,
+            2 => Self::WriteAheadLog,
+            _ => Self::Unknown(v),
+        }
+    }
+}
+
 /// This struct will wrap our 32bit number allowing us
 /// to control how it gets used later.
 #[derive(Debug)]
@@ -39,12 +62,27 @@ impl TryFrom<u16> for PageSize {
     }
 }
 
+pub fn parse_header(bytes: &[u8]) -> Result<(PageSize, FormatVersion, FormatVersion), Error> {
+    // Check that the first 16 bytes match the header string
+    validate_magic_string(&bytes)?;
+    // capture the page size
+    let page_size = parse_page_size(bytes)?;
+    // capture the write format version
+    let write_version = FormatVersion::from(bytes[18]);
+    // capture the read format version
+    let read_version = FormatVersion::from(bytes[19]);
+
+    Ok((page_size, write_version, read_version))
+}
+
 /// Validate that the bytes provided match the special string
 /// at the start of Sqlite3 files
 pub fn validate_magic_string(bytes: &[u8]) -> Result<(), Error> {
     let buf = &bytes[0..16];
     if buf != HEADER_STRING {
-        return Err(Error::HeaderString(String::from_utf8_lossy(buf).to_string()));
+        return Err(Error::HeaderString(
+            String::from_utf8_lossy(buf).to_string(),
+        ));
     }
 
     Ok(())
@@ -54,8 +92,8 @@ pub fn validate_magic_string(bytes: &[u8]) -> Result<(), Error> {
 pub fn parse_page_size(bytes: &[u8]) -> Result<PageSize, Error> {
     // Convert into array, and convert error if needed, so that the `?` operator works
     let page_size_bytes: [u8; 2] = bytes[16..18].try_into().map_err(|_| {
-       Error::InvalidPageSize(format!("expected a 2 byte slice, found: {:?}", bytes))
+        Error::InvalidPageSize(format!("expected a 2 byte slice, found: {:?}", bytes))
     })?;
 
     u16::from_be_bytes(page_size_bytes).try_into()
-}
\ No newline at end of file
+}
diff --git a/src/lib.rs b/src/lib.rs
index f8da16c..8f708c2 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,2 +1,2 @@
 pub mod error;
-pub mod header;
\ No newline at end of file
+pub mod header;
diff --git a/src/main.rs b/src/main.rs
index 19e7056..ba902eb 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,5 +1,5 @@
 use sqlite_parser::{
-    header::{validate_magic_string, parse_page_size},
+    header::parse_header,
     error::Error,
 };
 use std::fs::read;
@@ -7,13 +7,12 @@ use std::fs::read;
 fn main() -> Result<(), Error> {
     // first, read in all the bytes of our file
     // using unwrap to just panic if this fails
-    let contents = read("data.sqlite").unwrap();
+    let contents = read("data.sqlite")
+        .expect("Failed to read data.sqlite");
 
-    validate_magic_string(&contents)?;
+    let (page_size, write_format, read_format) = parse_header(&contents[0..100])?;
 
-    let page_size = parse_page_size(&contents)?;
-
-    println!("{:?}", page_size);
+    println!("page_size {:?}, write_format {:?}, read_format {:?}", page_size, write_format, read_format);
 
     Ok(())
 }