Demo rust program to walk over mbox files.

.gitignore

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+/target
+**/*.rs.bk

Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "base64"
+version = "0.10.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "byteorder 1.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "byteorder"
+version = "1.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "cfg-if"
+version = "0.1.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "charset"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "base64 0.10.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "encoding_rs 0.8.20 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "email"
+version = "0.1.0"
+dependencies = [
+ "mailparse 0.9.2 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "encoding_rs"
+version = "0.8.20"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "cfg-if 0.1.10 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "mailparse"
+version = "0.9.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "base64 0.10.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "charset 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quoted_printable 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "quoted_printable"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[metadata]
+"checksum base64 0.10.1 (registry+https://github.com/rust-lang/crates.io-index)" = "0b25d992356d2eb0ed82172f5248873db5560c4721f564b13cb5193bda5e668e"
+"checksum byteorder 1.3.2 (registry+https://github.com/rust-lang/crates.io-index)" = "a7c3dd8985a7111efc5c80b44e23ecdd8c007de8ade3b96595387e812b957cf5"
+"checksum cfg-if 0.1.10 (registry+https://github.com/rust-lang/crates.io-index)" = "4785bdd1c96b2a846b2bd7cc02e86b6b3dbf14e7e53446c4f54c92a361040822"
+"checksum charset 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "4f426e64df1c3de26cbf44593c6ffff5dbfd43bbf9de0d075058558126b3fc73"
+"checksum encoding_rs 0.8.20 (registry+https://github.com/rust-lang/crates.io-index)" = "87240518927716f79692c2ed85bfe6e98196d18c6401ec75355760233a7e12e9"
+"checksum mailparse 0.9.2 (registry+https://github.com/rust-lang/crates.io-index)" = "51a60bad00d8aa905d31cf239f207ad4ef16c963ea53cf522d5fd7dc7f3ecfe2"
+"checksum quoted_printable 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)" = "86cedf331228892e747bb85beb130b6bb23fc628c40dde9ea01eb6becea3c798"

Cargo.toml

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+[package]
+name = "email"
+version = "0.1.0"
+authors = ["Bill Thiede <git@xinu.tv>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+mailparse = "0.9.2"

src/main.rs

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+use std::env;
+use std::error::Error;
+use std::fs::File;
+use std::io::prelude::*;
+use std::process::exit;
+use std::slice::Iter;
+
+use mailparse::dateparse;
+use mailparse::MailHeaderMap;
+
+fn newline(b: &u8) -> bool {
+    *b == b'\n'
+}
+
+fn index_of(it: &mut Iter<u8>, needle: &[u8]) -> Option<usize> {
+    let mut needle_ix = 0;
+    it.position(move |&b| {
+        if b == needle[needle_ix] {
+            needle_ix += 1;
+            if needle_ix == needle.len() {
+                return true;
+            }
+        } else if b == needle[0] {
+            needle_ix = 1;
+        } else {
+            needle_ix = 0;
+        }
+        false
+    })
+}
+
+fn parse_mbox(mbox_bytes: &Vec<u8>) -> Result<(), Box<dyn Error>> {
+    let mut it = mbox_bytes.iter();
+    let mut ix = 0;
+
+    loop {
+        let mail_start = it.position(newline);
+        if mail_start.is_none() {
+            return Ok(());
+        }
+        ix += mail_start.unwrap() + 1;
+        let start = ix;
+
+        let delim = b"\nFrom ";
+        let next_mail_start = index_of(&mut it, delim);
+
+        let end = match next_mail_start {
+            Some(x) => {
+                ix += x + 1;
+                ix - delim.len()
+            }
+            None => mbox_bytes.len(),
+        };
+
+        let mail_bytes = &mbox_bytes[start..end];
+
+        let mail = mailparse::parse_mail(mail_bytes).unwrap();
+        println!(
+            "{:?} {:?} from {:?}",
+            match mail.headers.get_first_value("Date")? {
+                Some(date) => date,
+                None => "NO DATE".to_string(),
+            },
+            match mail.headers.get_first_value("Subject")? {
+                Some(subject) => subject,
+                None => "NO SUBJECT".to_string(),
+            },
+            match mail.headers.get_first_value("From")? {
+                Some(from) => from,
+                None => "NO FROM".to_string(),
+            },
+        );
+    }
+}
+
+fn main() {
+    if env::args().count() <= 1 {
+        println!("Provide mbox files as arguments");
+        exit(1);
+    }
+    let mut args = env::args();
+    args.next(); // drop executable name
+    args.for_each(|mbox_path| {
+        let mut mbox = File::open(mbox_path).unwrap();
+        let mut mails = Vec::new();
+        mbox.read_to_end(&mut mails).unwrap();
+        parse_mbox(&mails);
+    });
+}