Add functionality to handle JSON doc child inscriptions as special case

Why:
- Some generative art collections have inscribed all art within a single
parent inscription to save considerable storage space on the
blockchain.
- The ord explorer is unable to currently support collections inscribed
  in this manner.  This commit adds this support.

What:
- In order to support these generative art collections, we need to be able
  to inscribe the metadata for children in an agreed upon JSON spec.
- These child inscriptions are JSON documents containing url parameters
  that instruct the parent inscription to
  render a specific item in the collection.

How:
- Since all art is contained in the parent, we added a simple redirect to
  render the parent inscription with included url parameters.
- There are 3 constraints which must be in the child inscription before
  the redirect can happen:
1. The child inscription must have a parent inscription.
2. The child inscription's body data must be valid JSON.
3. The child inscription's body JSON data must contain a field named
   "is_ord_pointer", with any value.

Proposed JSON standard:
```
{
   "is_pointer": 1,
   "url_params": ["tokenID=4969"],
}
```

Related Issue:
- https://github.com/casey/ord/issues/783

Co-authored-by: Clarke Plumo <[email protected]>

src/subcommand/server.rs

@@ -1,3 +1,5 @@
+use serde_json::{Value};
+
 use {
   self::{
     deserialize_from_str::DeserializeFromStr,
@@ -734,6 +736,10 @@ impl Server {
       .get_inscription_by_id(inscription_id)?
       .ok_or_not_found(|| format!("inscription {inscription_id}"))?;
 
+    if let Some(response) = Self::get_content_response_if_child_pointer(&inscription) {
+      return response;
+    }
+
     Ok(
       Self::content_response(inscription)
         .ok_or_not_found(|| format!("inscription {inscription_id} content"))?
@@ -764,6 +770,45 @@ impl Server {
     Some((headers, inscription.into_body()?))
   }
 
+  fn get_parent_url_params_if_child_pointer(inscription: &Inscription) -> Option<String> {
+    if !inscription.get_parent_id().is_some() {
+      return None;
+    }
+
+    if !Self::valid_json(inscription.body()) {
+      return None;
+    }
+
+    let json_result: Result<Value, serde_json::Error> = serde_json::from_slice(&inscription.body().unwrap());
+    let json: Value = json_result.unwrap();
+
+    if !json.as_object().unwrap().contains_key("is_pointer") {
+      return None;
+    }
+
+    let parent_url_params = Self::get_url_params_from_json_value(json);
+
+    Some(parent_url_params)
+  }
+
+  fn get_content_response_if_child_pointer(inscription: &Inscription) -> Option<ServerResult<Response>> {
+    let parent_url_params = Self::get_parent_url_params_if_child_pointer(inscription);
+    if let Some(url_params) = parent_url_params {
+      let redirect_uri = format!("/content/{}?{}", inscription.get_parent_id().unwrap(), url_params);
+      return Some(Ok(Redirect::temporary(&redirect_uri).into_response()));
+    }
+    None
+  }
+
+  fn get_preview_response_if_child_pointer(inscription: &Inscription) -> Option<ServerResult<Response>> {
+    let parent_url_params = Self::get_parent_url_params_if_child_pointer(inscription);
+    if let Some(url_params) = parent_url_params {
+      let redirect_uri = format!("/preview/{}?{}", inscription.get_parent_id().unwrap(), url_params);
+      return Some(Ok(Redirect::temporary(&redirect_uri).into_response()));
+    }
+    None
+  }
+
   async fn preview(
     Extension(index): Extension<Arc<Index>>,
     Extension(config): Extension<Arc<Config>>,
@@ -777,6 +822,10 @@ impl Server {
       .get_inscription_by_id(inscription_id)?
       .ok_or_not_found(|| format!("inscription {inscription_id}"))?;
 
+    if let Some(response) = Self::get_preview_response_if_child_pointer(&inscription) {
+      return response;
+    }
+
     match inscription.media() {
       Media::Audio => Ok(PreviewAudioHtml { inscription_id }.into_response()),
       Media::Iframe => Ok(
@@ -821,6 +870,28 @@ impl Server {
     }
   }
 
+  fn valid_json(data: Option<&[u8]>) -> bool {
+    match data {
+      Some(bytes) => serde_json::from_slice::<Value>(bytes).is_ok(),
+      None => false,
+    }
+  }
+
+  fn get_url_params_from_json_value(json: Value) -> String {
+    let mut params_str = String::new();
+    if let Some(url_params_field) = json.get("url_params") {
+      if let Some(url_params) = url_params_field.as_array() {
+        for param in url_params {
+          if !params_str.is_empty() {
+            params_str.push('&');
+          }
+          params_str.push_str(&param.as_str().unwrap());
+        }
+      }
+    }
+    params_str
+  }
+
   async fn inscription(
     Extension(page_config): Extension<Arc<PageConfig>>,
     Extension(index): Extension<Arc<Index>>,