Add tags chapter

book/04-events.md

@@ -38,8 +38,16 @@ use sha2::{Digest, Sha256};
 use std::fmt;
 
 use crate::keys::PublicKey;
+use crate::tags::Tags;
 ```
 
+The `Tag` and `Tags` types are introduced in the next chapter. For
+this chapter, treat `Tag` as a transparent wrapper around
+`Vec<String>` and `Tags` as a transparent wrapper around `Vec<Tag>` —
+serde sees them as bare arrays, the canonical form hashes identically,
+and you can build them with `Tag::new("t", ["nostr"])` and
+`Tags::from(vec![...])`.
+
 ## Errors
 
 ```rust {file=coracle-lib/src/events.rs}
@@ -104,12 +112,12 @@ metadata in the "could be added later" sense.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct EventContent {
     pub content: String,
-    pub tags: Vec<Vec<String>>,
+    pub tags: Tags,
 }
 
 impl EventContent {
-    pub fn new(content: impl Into<String>, tags: Vec<Vec<String>>) -> Self {
-        EventContent { content: content.into(), tags }
+    pub fn new(content: impl Into<String>, tags: impl Into<Tags>) -> Self {
+        EventContent { content: content.into(), tags: tags.into() }
     }
 }
 ```
@@ -126,7 +134,7 @@ which kinds mean what — that's the next layer of the stack.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct EventTemplate {
     pub content: String,
-    pub tags: Vec<Vec<String>>,
+    pub tags: Tags,
     pub kind: u16,
 }
 
@@ -151,7 +159,7 @@ it is.
 pub struct StampedEvent {
     pub content: String,
     pub kind: u16,
-    pub tags: Vec<Vec<String>>,
+    pub tags: Tags,
     pub created_at: u64,
 }
 
@@ -179,7 +187,7 @@ claims responsibility for.
 pub struct OwnedEvent {
     pub content: String,
     pub kind: u16,
-    pub tags: Vec<Vec<String>>,
+    pub tags: Tags,
     pub created_at: u64,
     pub pubkey: PublicKey,
 }
@@ -216,7 +224,7 @@ fn canonical(
     pubkey: &PublicKey,
     created_at: u64,
     kind: u16,
-    tags: &[Vec<String>],
+    tags: &Tags,
     content: &str,
 ) -> String {
     serde_json::json!([
@@ -235,7 +243,7 @@ fn canonical(
 pub struct HashedEvent {
     pub content: String,
     pub kind: u16,
-    pub tags: Vec<Vec<String>>,
+    pub tags: Tags,
     pub created_at: u64,
     pub pubkey: PublicKey,
     pub id: [u8; 32],
@@ -271,7 +279,7 @@ wire.
 pub struct Event {
     pub content: String,
     pub kind: u16,
-    pub tags: Vec<Vec<String>>,
+    pub tags: Tags,
     pub created_at: u64,
     pub pubkey: PublicKey,
     pub id: [u8; 32],
@@ -423,7 +431,7 @@ impl<'de> Visitor<'de> for EventVisitor {
         let mut pubkey: Option<String> = None;
         let mut created_at: Option<u64> = None;
         let mut kind: Option<u16> = None;
-        let mut tags: Option<Vec<Vec<String>>> = None;
+        let mut tags: Option<Tags> = None;
         let mut content: Option<String> = None;
         let mut sig: Option<String> = None;