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Using HTTP/1.1 Caching Headers

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Since request header field is used with a method to make it conditional. If the requested object has not been modified since the time specified in this field, DX Storage will perform the requested operation as if the If-Unmodified-Since header were not present. If the requested object has been modified since the specified time, DX Storage will not perform the requested operation, and instead return a 412 Precondition failed. If the specified date is invalid, the header is ignored. 18.2.4. Expires DX Storage returns an Expires header if it is persisted with your content. DX Storage does not generate an Expires header. The Expires header field gives the date/time after which the response is considered stale. A stale cache entry may not normally be returned by a cache (either a proxy cache or a user agent cache) unless it is first validated with DX Storage (or with an intermediate cache that has a fresh copy of the object). Since DX Storage has no information about when an anchor stream might be updated, and little information about when an object might be deleted, DX Storage does not generate an Expires header for any object. However, Expires will be added to the list of persisted headers so that applications can supply a hint to caching proxies and clients as to when an object might become stale. 18.3. Using HTTP/1.1 Caching Headers The newer HTTP/1.1 cache coherency mechanism does not use dates or time stamps and thus avoids the granularity and synchronization problems of the HTTP/1.0 headers. Instead, it uses "entity tags" or ETags which can only be compared for exact equality. In DX Storage, ETag values are opaque, variable length, case-sensitive strings that must be enclosed in quotes. Any characters preceding or following the quoted string will be ignored. If the header value has no quoted string, the entire header will be ignored. Note Because DX Storage is merely storing data rather than dynamically generating it, the fine-grained control allowed in the Cache-Control header is not implemented at this time. However, if supplied by an application, the Cache-Control header will be stored by DX Storage and then returned as-is by the server. 18.3.1. ETag DX Storage will return the ETag header for all POST, PUT, GET, and HEAD operations. DX Storage will use only "strong" ETags as defined in RFC2616, which can only be compared for exact (casesensitive) equality. Example ETag response header: ETag: "508941dc9b52243f64d964b058354b76" The ETag of an ordinary object never changes during the entire lifecycle of the object, whereas anchor stream ETags will change each time the object is mutated by a PUT. 18.3.2. If-Match A DX Storage client or proxy can include this header with any request method. The value of the header is either a single quoted string (possibly with some ignored flags outside the quotation marks), a comma separated list of quoted strings, or a single asterisk, anything after which will be ignored. Copyright © 2010 Caringo, Inc. All rights reserved 67 Version 5.0 December 2010

Section	Page
DX Object Storage Application Guide	1
Table of Contents	3
Chapter 1. Introduction to DX Storage Objects	6
1.1. Introducing Named Objects	6
1.2. Summary of Named Objects and Unnamed Objects	7
1.3. Common Named Object Terminology	7
1.4. About DX Storage Object Types	8
1.5. Bucket and Object Naming Rules	8
1.6. Simple Examples of Creating Buckets and Named Objects	8
1.7. Universal Resource Identifiers (URIs)	9
1.8. About Objects and Security	10
1.8.1. The Basics of DX Storage Security	10
1.8.2. Commonly Used Security Terminology	11
1.8.3. Basic Security Guidelines	11
1.9. Concepts for Unnamed Objects	11
1.9.1. Universally Unique Identifiers (UUIDs)	11
1.9.2. About Immutable Objects	12
1.9.3. About Anchor Streams	12
1.10. Document Typographical Conventions	13
Chapter 2. Connecting to a DX Storage Cluster	14
2.1. About the Primary Access Node (PAN)	14
2.2. Requirements for Node Accessibility	14
2.2.1. Using the DX Storage Software Development Kit (SDK)	14
2.2.2. Using Multicast-DNS (mDNS)	15
2.2.3. Using DNS Round Robin	15
2.2.4. Using a Pool of Static IP Addresses	16
2.2.5. Using a Single Static IP Address	16
Chapter 3. Application Best Practices	17
3.1. Using the Software Development Kit (SDK)	17
3.2. Dynamically Locating DX Storage Nodes	17
3.3. Optimizing Bucket and Domain Operations	17
3.4. Using HTTP Client Libraries	17
3.5. Handling Redirects	18
3.6. Using Range Headers	18
3.7. Multi-Threading	19
3.8. Using Persistent Connections	19
Chapter 4. Introduction to the Simple Content Storage Protocol (SCSP)	20
4.1. Mapping SCSP Operations to HTTP Methods	20
4.2. HTTP Overview	21
4.3. Requests and Responses	21
4.3.1. HTTP Response Codes	21
4.3.2. Redirect Responses	22
4.4. Formatting SCSP Commands for Named and Unnamed Objects	22
4.5. Undefined Responses from DX Storage	23
4.6. Normal Response Headers	24
Chapter 5. SCSP READ	27
5.1. Introduction to READ	27
5.1.1. Reading With Content Validation	27
5.1.2. Requestion Node Status and Cluster Capacity	27
5.2. Unnamed Object READ Details	28
5.3. Normal Responses to READ	28
5.3.1. Normal READ Responses for Named Objects	28
5.3.1.1. Normal READ Response for a Domain	28
5.3.1.2. Normal READ Response for a Bucket	29
5.3.1.3. Normal READ Response for a Named Object	29
5.3.2. Normal READ Response for Unnamed Objects	29
5.3.3. Other Normal READ Responses	30
5.4. Error Responses to READ	30
Chapter 6. SCSP WRITE	32
6.1. Introduction to WRITE	32
6.1.1. About the Expect: 100-continue Header and WRITE	33
6.1.2. About Replicate On Write	33
6.2. Named Object WRITE Details	33
6.3. Unnamed Object WRITE Details	33
6.4. Normal Responses to WRITE	33
6.5. Error Responses to WRITE	34
Chapter 7. SCSP DELETE	36
7.1. Introduction to DELETE	36
7.2. Unnamed Object DELETE Details	37
7.3. Named Object DELETE Details	37
7.4. Normal Responses to DELETE	37
7.5. Error Responses to DELETE	38
Chapter 8. SCSP UPDATE	39
8.1. Introduction to UPDATE	39
8.2. Unnamed Object UPDATE Details	39
8.3. Normal Responses to UPDATE	40
Chapter 9. SCSP COPY	41
9.1. Introduction to COPY	41
9.2. Unnamed Object COPY Details	41
9.3. Normal Responses to COPY	41
Chapter 10. SCSP APPEND	42
10.1. Introduction to APPEND	42
10.2. Unnamed Object APPEND Details	43
10.3. Normal Responses to APPEND	43
Chapter 11. SCSP INFO	44
11.1. Introduction to INFO	44
11.1.1. Getting Replica Counts	44
11.1.2. Getting Node Status and Cluster Capacity	44
11.2. Unnamed Object INFO Details	45
11.3. Normal Responses to INFO	45
11.3.1. Normal INFO Responses for Named and Unnamed Objects	45
11.3.2. Normal INFO Responses for Named Objects	46
11.3.3. Normal INFO Responses for Unnamed Objects	47
11.4. Error Responses to INFO	47
Chapter 12. Introduction to Object Security	48
12.1. About Security Roles	48
12.2. Security Realm Overview	49
12.2.1. Common Security Terminology	49
12.2.2. About Security Realms	49
12.2.3. About Realm Caching and Security	49
12.3. About Authorization Header Syntax	50
12.3.1. About Realm Names	51
12.3.1.1. About Realms and Buckets	51
12.3.1.2. About owner@ and @owner Syntax	51
12.3.1.3. About user@realm Syntax	51
12.4. Authorization Specification Examples	51
12.5. About Authorization Header Evaluation	52
12.6. Creating Realms	53
12.7. Updating the Realm on a Bucket	54
12.8. Administrative Override and Security	54
Chapter 13. Managing Security for Application Developers	55
13.1. What Application Developers Need to Know	55
13.2. About Bucket Authorization	55
13.3. Example: Creating Bucket Owners	56
13.4. Examples of Creating Buckets and Named Objects	56
Chapter 14. Managing Security for Domain Managers	59
14.1. What Domain Managers Need to Know	59
14.2. About Domain Manager Tasks and Responsibilities	59
14.3. Examples of Updating Domain and Administrator User Lists	59
14.3.1. Updating the Domain Realm	60
14.3.2. Updating the Domain Manager Realm	61
14.3.3. Updating a Realm Using PUT	62
Chapter 15. Using the Content-MD5 Metadata Header	64
Chapter 16. Using Lifepoint Metadata Headers	65
16.1. About Storage Policies	65
16.2. A Simple Lifecycle Example	65
16.3. Lifepoint/Lifecycle Specification	66
16.4. Constraint Types	66
16.4.1. Replication	67
16.4.2. Deletion	67
Chapter 17. Using the Allow Metadata Header	69
17.1. Overview of the Allow Header	69
17.2. Administrative Override	69
Chapter 18. Using Caching Metadata Headers	71
18.1. About Caching Headers	71
18.2. Using HTTP/1.0 Caching Headers	71
18.2.1. Last-Modified	71
18.2.2. If-Modified-Since	71
18.2.3. If-Unmodified-Since	71
18.2.4. Expires	72
18.3. Using HTTP/1.1 Caching Headers	72
18.3.1. ETag	72
18.3.2. If-Match	72
18.3.3. If-None-Match	73
18.3.4. If-Range	73
Chapter 19. Using Custom Metadata Headers	75
Chapter 20. Basic Content Integrity Assurance	76
20.1. Integrity Seals	76
20.2. Validating Reads	76
20.3. Application Initiated Hash Upgrading	77
Appendix A. Content Header Metadata	78
Appendix B. Sample Code and Client Library Behaviors with 100-Continue	80

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Version 5.0

December 2010

Since request header field is used with a method to make it conditional. If the requested object

has not been modified since the time specified in this field, DX Storage will perform the requested

operation as if the If-Unmodified-Since header were not present. If the requested object has been

modified since the specified time, DX Storage will not perform the requested operation, and instead

return a 412 Precondition failed. If the specified date is invalid, the header is ignored.

18.2.4. Expires

DX Storage returns an

Expires header

if it is persisted with your content. DX Storage does not

generate an Expires header.

The Expires header field gives the date/time after which the response is considered stale. A stale

cache entry may not normally be returned by a cache (either a proxy cache or a user agent cache)

unless it is first validated with DX Storage (or with an intermediate cache that has a fresh copy of

the object). Since DX Storage has no information about when an anchor stream might be updated,

and little information about when an object might be deleted, DX Storage does not generate an

Expires header for any object. However, Expires will be added to the list of persisted headers

so that applications can supply a hint to caching proxies and clients as to when an object might

become stale.

18.3. Using HTTP/1.1 Caching Headers

The newer HTTP/1.1 cache coherency mechanism does not use dates or time stamps and thus

avoids the granularity and synchronization problems of the HTTP/1.0 headers. Instead, it uses

"entity tags" or ETags which can only be compared for exact equality. In DX Storage, ETag values

are opaque, variable length, case-sensitive strings that must be enclosed in quotes. Any characters

preceding or following the quoted string will be ignored. If the header value has no quoted string, the

entire header will be ignored.

Note

Because DX Storage is merely storing data rather than dynamically generating it, the

fine-grained control allowed in the Cache-Control header is not implemented at this time.

However, if supplied by an application, the Cache-Control header will be stored by DX

Storage and then returned as-is by the server.

18.3.1. ETag

DX Storage will return the ETag header for all POST, PUT, GET, and HEAD operations. DX Storage

will use only "strong" ETags as defined in RFC2616, which can only be compared for exact (case-

sensitive) equality.

Example ETag response header:

ETag: "508941dc9b52243f64d964b058354b76"

The ETag of an ordinary object never changes during the entire lifecycle of the object, whereas

anchor stream ETags will change each time the object is mutated by a PUT.

18.3.2. If-Match

A DX Storage client or proxy can include this header with any request method. The value of the

header is either a single quoted string (possibly with some ignored flags outside the quotation

marks), a comma separated list of quoted strings, or a single asterisk, anything after which will be

ignored.