Use git-style subdirectories for data files.

- To address scalability concerns, we put data files into
    subdirectories by splitting e.g. the fingerprint into a two
    character prefix and the rest, using the prefix as subdirectory
    name, and the rest as filename.

  - We hide this fact from the user using rewrite rules in nginx.

  - Fixes #38.

nginx.conf

@@ -21,19 +21,22 @@ http {
 
     root dist/public;
 
-    location ^~ /by-email/ {
+    location /by-email/ {
+      rewrite ^/by-email/([^/][^/])(..*)$ /by-email/$1/$2 break;
       default_type application/pgp-keys;
-      try_files /$request_uri =404;
+      try_files /$uri =404;
     }
 
-    location ^~ /by-fingerprint/ {
+    location /by-fingerprint/ {
+      rewrite ^/by-fingerprint/([^/][^/])(..*)$ /by-fingerprint/$1/$2 break;
       default_type application/pgp-keys;
-      try_files /$request_uri =404;
+      try_files /$uri =404;
     }
 
-    location ^~ /by-keyid/ {
+    location /by-keyid/ {
+      rewrite ^/by-keyid/([^/][^/])(.*)$ /by-keyid/$1/$2 break;
       default_type application/pgp-keys;
-      try_files /$request_uri =404;
+      try_files /$uri =404;
     }
 
     location = / {

src/database/fs.rs

@@ -94,17 +94,23 @@ impl Filesystem {
 
     /// Returns the path to the given KeyID.
     fn path_to_keyid(&self, keyid: &KeyID) -> PathBuf {
-        self.base_by_keyid.join(keyid.to_string())
+        let hex = keyid.to_string();
+        self.base_by_keyid.join(&hex[..2]).join(&hex[2..])
     }
 
     /// Returns the path to the given Fingerprint.
     fn path_to_fingerprint(&self, fingerprint: &Fingerprint) -> PathBuf {
-        self.base_by_fingerprint.join(fingerprint.to_string())
+        let hex = fingerprint.to_string();
+        self.base_by_fingerprint.join(&hex[..2]).join(&hex[2..])
     }
 
     /// Returns the path to the given Email.
     fn path_to_email(&self, email: &str) -> PathBuf {
-        self.base_by_email.join(email.to_string())
+        if email.len() > 2 {
+            self.base_by_email.join(&email[..2]).join(&email[2..])
+        } else {
+            self.base_by_email.join(email)
+        }
     }
 
     fn new_token<'a>(&self, base: &'a str) -> Result<(File, String)> {